diff --git a/appendix_b.txt b/appendix_b.txt new file mode 100644 index 0000000..a2fa28f --- /dev/null +++ b/appendix_b.txt @@ -0,0 +1 @@ +898 diff --git a/chapter_1/examples.md b/chapter_1/examples.md new file mode 100644 index 0000000..0ef0a52 --- /dev/null +++ b/chapter_1/examples.md @@ -0,0 +1,424 @@ +**Example 1.1.1** + +Page 24 + +Use variables to rewrite the following sentences more formally. + +a. Are there numbers with the property that the sum of their squares equals the +square of their sum? + +b. Given any real number, its square is nonnegative. + +**Solution** + +a. Are there numbers $a$ and $b$ with the property that $a^2 + b^2 = (a + b)^2$? + +_Or_: Are there numbers $a$$ and $b$ such that $a^2 + b^2 = (a + b)^2$? + +_Or_: Do there exist any numbers $a$ and $b$ such that $a^2 + b^2 = (a + b)^2$? + +b. Given any real number $r$, $r^2$ is nonnegative. + +_Or_: For any real number $r$, $r^2 \geq 0$. + +_Or_: For every real number $r$, $r^2 \geq 0$. + +--- + +**Example 1.1.2** + +Page 26 + +Fill in the blanks to rewrite the following statement: + +For every real number $x$, if $x$ is nonzero then $x^2$ is positive. + +a. If a real number is nonzero, then its square ________. + +b. For every nonzero real number $x$, ________. + +c. If $x$ ________, then ________. + +d. The square of any nonzero real number is ________. + +e. All nonzero real numbers have ________. + +**Solution**. + +a. is positive. + +b. $x^2$ is positive. + +c. is a nonzero real number, $x^2$ is positive. + +d. positive. + +e. positive squares . + +--- + +**Example 1.1.3** + +Page 27 + +Fill in the blanks to rewrite the following statement: Every pot has a lid. + +a. All pots ________. + +b. For every pot $P$, there is ________. + +c. For every pot $P$, there is a lid $L$ such that ________. + +**Solution** + +a. have lids. + +b. a lid. + +c. $L$ is a lid for $P$.. + +--- + +**Example 1.1.4** + +Page 28 + +Fill in the blanks to rewrite the following statement in three different ways: + +There is a person in my class who is at least as old as every person in my clas. + +a. Some ________ is at least as old as ________. + +b. There is a person $p$ in my class such that $p$ is ________. + +c. There is a person $p$ in my class with the property that for every person $q$ +in my class, $p$ is ________. + +**Solution** + +a. person; every person. + +b. at least as old as every person in my class. + +c. at least as old as $q$. + +--- + +**Example 1.2.1** + +Page 30 + +**Using the Set-Roster Notation** + +a. Let $A = \{1, 2, 3\}$, $B = \{3, 1, 2\}$, and $C = \{1, 1, 2, 3, 3, 3\}$. +What are the elements of $A$, $B$, and $C$? How are $A$, $B$, and $C$ related? + +b. Is $\{0\} = 0$? + +c. How many elements are in the set $\{1, \{1}\}$? + +d. For each nonnegative integer $n$, let $U_n = \{n, -n\}$. Find $U_1$, $U_2$, +and $U_0$. + +**Solution** + +a. Let $A = \{1, 2, 3\}$, $B = \{3, 1, 2\}$, and $C = \{1, 1, 2, 3, 3, 3\}$. +What are the elements of $A$, $B$, and $C$? How are $A$, $B$, and $C$ related? + +$A$, $B$, and $C$ have exactly the same three elements, $1$, $2$, and $3$. +Therefore, $A$, $B$, and $C$ are simply different ways to represent the same +set. + +b. Is $\{0\} = 0$? + +$\{0\} \neq 0$ because $\{0\}$ is a set with one element, namely $0$, whereas +$0$ is just the symbol that represents the number zero. + +c. How many elements are in the set $\{1, \{1}\}$? + +The set $\{1, \{1\}\}$ has two elements. $1$ and the set whose only element is +$1$. + +d. For each nonnegative integer $n$, let $U_n = \{n, -n\}$. Find $U_1$, $U_2$, +and $U_0$. + +$U_1 = \{1, -1\}, \quad U_2 = \{2, -2\}, \quad U_0 = \{0, 0\} = \{0\}$ + +--- + +**Example 1.2.2** + +Page 31 + +**Using the Set-Builder Notation** + +Given that $\mathbb{R}$ denotes the set of all real numbers, $\mathbb{Z}$ the +set of all integers, and $\mathbb{Z}^+$ the set of all positive integers, +describe each of the following sets. + +a. $\{x \in \mathbb{R} | -2 < x < 5\}$ + +b. $\{x \in \mathbb{Z} | -2 < x < 5\}$ + +c. $\{x \in \mathbb{Z}^+ | -2 < x < 5\}$ + +**Solution** + +a. $\{x \in \mathbb{R} | -2 < x < 5\}$ + +$\{x \in \mathbb{R} | -2 < x < 5\}$ is the open interval of real numbers +(strictly) between $-2$ and 5. It is pictured as follows (see page 31). + +b. $\{x \in \mathbb{Z} | -2 < x < 5\}$ + +$\{x \in \mathbb{Z} | -2 < x < 5\}$ is the set of all integers (strictly) +between $-2$ and $5$. It is equal to the set $\{-1, 0, 1, 2, 3, 4}$. + +c. $\{x \in \mathbb{Z}^+ | -2 < x < 5\}$ + +Since all the integers in $\mathbb{Z}^+$ are positive, +$\{x \in \mathbb{Z}^+ | -2 < x < 5\} = \{1, 2, 3, 4\}$. + +--- + +**Example 1.2.3** + +Page 32 + +Let $A = \mathbb{Z}^+$, $B = \{n \in \mathbb{Z} | 0 \leq n \leq 100\}$, and +$C = \{100, 200, 300, 400, 500\}$. Evaluate the truth and falsity of each of the +following statements + +a. $B \subseteq A$ + +b. $C$ is a proper subset of $A$. + +c. $C$ and $B$ have at least one element in common + +d. $C \subseteq B$ + +e. $C \subseteq C$ + +**Solution** + +a. $B \subseteq A$ + +False. Zero is not a positive integer. Thus zero is in $B$ but zero is not in +$A$, and so $B \nsubseteq A$ + +b. $C$ is a proper subset of $A$. + +True. Each element in $C$ is a positive integer, and hence, is in $A$, but there +are elements in $A$ that are not in $C$. For instance, $1$ is in $A$ and not in +$C$. + +c. $C$ and $B$ have at least one element in common + +True. For example, $100$ is in both $C$ and $B$. + +d. $C \subseteq B$ + +False. For example, $200$ is in $C$ but not in $B$. + +e. $C \subseteq C$ + +True. Every element in $C$ is in $C$. In general, the definition of a subset +implies that all sets are subsets of themselves. + +--- + +**Example 1.2.4** + +Page 33 + +**Distinction between $\in$ and $\subseteq$** + +Which of the following are true statements? + +a. $2 \in \{1, 2, 3\}$ + +b. $\{2\} \in \{1, 2, 3\}$ + +c. $2 \subseteq \{1, 2, 3\}$ + +d. $\{2\} \subseteq \{1, 2, 3\}$ + +e. $\{2\} \subseteq \{\{1\}, \{2\}\}$ + +f. $\{2} \in \{\{1\}, \{2\}\}$ + +**Solution** + +Only (a), (d), and (f) are true. + +For (b) to be true, the set $\{1, 2, 3\}$ would have to contain the element +$\{2\}$. But the only elements of $\{1, 2, 3\}$ are $1$, $2$, and $3$, and $2$ +is not equal to $\{2\}$. Hence (b) is false. + +For \(c\) to be true, the number $2$ would have to be a set and every element in +the set $2$ would have to be an element of $\{1, 2, 3}$. This is not the case, +so \(c\) is false. + +For (e) to be true, every element in the set containing only the number $2$ +would have to be an element of the set whose elements are $\{1\}$ and $\{2\}$. +But $2$ is not equal to either $\{1\}$ or $\{2\}$, and so (e) is false. + +--- + +**Example 1.2.5 Ordered Pairs** + +Page 34 + +a. Is $(1, 2) = (2, 1)$? + +b. Is $\left(3, \dfrac{5}{10}\right) = \left(\sqrt{9}, \dfrac{1}{2}\right)$? + +c. What is the first element of $(1, 1)$? + +**Solution** + +a. Is $(1, 2) = (2, 1)$? + +No, By definition of equality of ordered pairs, + +$(1, 2) = (2, 1)$ if, and only if, 1 = 2, and 2 = 1. + +But $1 \neq 2$, and so the ordered pairs are not equal. + +b. Is $\left(3, \dfrac{5}{10}\right) = \left(\sqrt{9}, \dfrac{1}{2}\right)$? + +Yes. By definition of equality of ordered pairs, + +$\left(3, \dfrac{5}{10}\right) = \left(\sqrt{9}, \dfrac{1}{2}\right)$ if, and +only if, $3 = \sqrt{9}$ and $\dfrac{5}{10} = \dfrac{1}{2}$. + +Because these equations are both true, the ordered pairs are equal. + +c. What is the first element of $(1, 1)$? + +In the ordered pair $(1, 1)$, the first and second elements are both $1$. + +--- + +**Example 1.2.6 Ordered $n$-tuples** + +Page 34 + +a. Is $(1, 2, 3, 4) = (1, 2, 4, 3)$? + +b. Is +$\left(3, (-2)^2, \dfrac{1}{2}\right) = \left(\sqrt{9}, 4, \dfrac{3}{6}\right)$? + +**Solution** + +a. Is $(1, 2, 3, 4) = (1, 2, 4, 3)$? + +No. By definition of equality of ordered 4-tuples, + +$$ (1, 2, 3, 4) = (1, 2, 4, 3) \leftrightarrow 1 = 1, 2 = 2, 3 = 4, and 4 = 3 $$ + +But $3 \neq 4$, and so the ordered 4-tuples are not equal. + +b. Is +$\left(3, (-2)^2, \dfrac{1}{2}\right) = \left(\sqrt{9}, 4, \dfrac{3}{6}\right)$? + +Yes. By definition of equality of ordered triples. + +$$ \left(3, (-2)^2, \frac{1}{2}\right) = \left(\sqrt{9}, 4, \frac{3}{6}\right) \leftrightarrow 3 = \sqrt{9} \text{ and } (-2)^2 = 4 \text{ and } \frac{1}{2} = \frac{3}{6} $$ + +Because these equations are all true, the two ordered triples are equal. + +--- + +**Example 1.2.7 Cartesian Products** + +Page 35 + +Let $A = \{x, y\}$, $B = \{1, 2, 3\}$, and $C = \{a, b\}$. + +a. Find $A \times B$. + +b. Find $B \times A$. + +c. Find $A \times A$. + +d. How many elements are in $A \times B$, $B \times A$, and $A \times A$? + +e. Find $(A \times B) \times C$ + +f. Find $A \times B \times C$ + +g. Let $\mathbb{R}$ denote the set of all real numbers. Describe +$\mathbb{R} times \mathbb{R}$. + +**Solution** + +a. Find $A \times B$. + +$$ A \times B = \{(x, 1), (y, 1), (x, 2), (y, 2), (x, 3), (y, 3)\} $$ + +b. Find $B \times A$. + +$$ B \times A = \{(1, x), (1, y), (2, x), (2, y), (3, x), (3, y)\} $$ + +c. Find $A \times A$. + +$$ A \times A = \{(x, x), (x, y), (y, x), (y, y)\} $$ + +d. How many elements are in $A \times B$, $B \times A$, and $A \times A$? + +$A \times B$ has 6 elements. Note that this is the number of elements in $A$ +times the number of elements in $B$. $B \times A$ has 6 elements, the number of +elements in $B$ times the number of elements in $A$. $A \times A$ has 4 +elements, the number of elements in $A$ times the number of elements in $A$. + +e. Find $(A \times B) \times C$ + +$$ (A \times B) \times C = \{(u, v) | u \in A \times B \text{ and } v \in C\} $$ + +By definition of Cartesian product. + +$$ (A \times B) \times C = \{((x, 1), a), ((x, 2), a), ((x, 3), a), ((y, 1), a), ((y, 2), a), ((y, 3), a), ((x, 1), b), ((x, 2), b), ((x, 3), b), ((y, 1), b), ((y, 2), b), ((y, 3), b)\} $$ + +f. Find $A \times B \times C$ + +The Cartesian product $A \times B \times C$ is superficially similar to but is +not quite the same mathematical object as $(A \times B) \times C$. +$(A \times B) \times C$ is a set of ordered pairs of which one element is itself +an ordered pair, whereas $A \times B \times C$ is a set of ordered triples. By +definition of Cartesian product, + +$$ A \times B \times C = \{(u, v, w) | u \in A, v \in B, \text{ and } w \in C\} $$ + +$$ A \times B \times C = \{(x, 1, a), (x, 2, a), (x, 3, a), (y, 1, a), (y, 2, a), (y, 3, a), (x, 1, b), (x, 2, b), (x, 3, b), (y, 1, b), (y, 2, b), (y, 3, b)\} $$ + +g. Let $\mathbb{R}$ denote the set of all real numbers. Describe +$\mathbb{R} times \mathbb{R}$. + +$\mathbb{R} \times \mathbb{R}$ is the set of all ordered pairs $(x, y)$ where +both $x$ and $y$ are real numbers. If horizontal and vertical axes are drawn on +a plane and a unit length is marked off, then each ordered pair in +$\mathbb{R} \times \mathbb{R}$ corresponds to a unique point in the plane, with +the first and second elements o the pair indicating, respectively, the +horizontal and vertical positions of the point. The term **Cartesian plane** is +often used to refer to a plane with this coordinate system, as illustrated in +Figure 1.2.1 (see page 36). + +--- + +**Example 1.2.8 Strings** + +Page 36 + +Let $A = \{a, b\}$. List all the strings of length 3 over $A$ with at least two +characters that are the same. + +**Solution** + +_aab, aba, baa, aaa, bba, bab, abb, bbb_ + +In computer programming it is important to distinguish among different kinds of +data structures and to respect the notations that are used for them. Similarly +in mathematics, it is important to distinguish among, say, _{a, b, c}, {{ab}, +c}, (a, b, c), (a, (b, c)), abc_ and so forth, because these are all +significantly different objects. diff --git a/chapter_1/exercises.md b/chapter_1/exercises.md new file mode 100644 index 0000000..c8dac7c --- /dev/null +++ b/chapter_1/exercises.md @@ -0,0 +1,755 @@ +**Exercise Set 1.1** + +Page 28 + +In each of 1-6, fill in the blanks using a variable or variables to rewrite the +given statement. + +1. Is there a real number whose square is $-1$? + +a. Is there a real number $x$ such that ______? + +b. Does there exist ______ such that $x^2 = -1$? + +**Solution** + +a. Is there a real number $x$ such that $x^2 = -1$? + +b. Does there exist a real number $x$ such that $x^2 = -1$? + +2. Is there an integer that has a remainder of $2$ when it is divided by $5$ and + a remainder of $3$ when it is divided by $6$? + +a. Is there an integer $n$ such that $n$ has ______? + +b. Does there exist ______ such that if $n$ is divided by $5$ the remainder is +$2$ and if ______? + +_Note: There are integers with this property. Can you think of one?_ + +**Solution** + +a. Is there an integer $n$ such that $n$ has a remainder of $2$ when $n$ is +divided by $5$ and a remainder of $3$ when $n$ is divided by $6$? + +b. Does there exist a number $n$ such that if $n$ is divided by $5$ the +remainder is $2$ and if $n$ is divided by $6$ the remainder is $3$? + +_Note: There are integers with this property. Can you think of one?_ + +$$ 27 \mod 5 = 2 $$ + +$$ 27 \mod 6 = 3 $$ + +3. Given any two distinct real numbers, there is a real number in between them. + +a. Given any two distinct real numbers $a$ and $b$, there is a real number $c$ +such that $c$ is ______. + +b. For any two ______, ______ such that $c$ is between $a$ and $b$. + +**Solution** + +a. Given any two distinct real numbers $a$ and $b$, there is a real number $c$ +such that $c$ is $a \leq c \leq b$. + +b. For any two distinct real numbers $a$ and $b$, there exists a real number $c$ +such that $c$ is between $a$ and $b$. + +4. Given any real number, there is a real number that is greater. + +a. Given any real number $r$, there is ______ $s$ such that $s$ is ______ + +b. For any ______, ______ such that $s > r$. + +**Solution** + +a. Given any real number $r$, there is a real number $s$ such that $s$ is +greater than $r$. + +b. For any real number $r$, there exists a real number $s$ such that $s > r$. + +5. The reciprocal of any positive real number is positive. + +a. Given any positive real number $r$, the reciprocal of ______. + +b. For any real number $$, if $r$ is ______, then ______. + +c. If a real number $r$ ______, then ______. + +**Solution** + +a. Given any positive real number $r$, the reciprocal of $r$ is positive. + +b. For any real number $r$, if $r$ is positive, then the reciprocal of $r$ is +positive. + +c. If a real number $r$ is positive, then the reciprocal of $r$ is positive. + +6. The cube root of any negative real number is negative. + +a. Given any negative real number $s$, the cube root of ______. + +b. For any real number $s$, if $s$ is ______, then ______. + +c. If a real number $s$ ______, then ______. + +**Solution** + +a. Given any negative real number $s$, the cube root of $s$ is negative. + +b. For any real number $s$, if $s$ is negative, then the cube root of $s$ is +negative. + +c. If a real number $s$ is negative, then the cube root of $s$ is negative. + +7. Rewrite the following statements less formally, without using variables. + Determine, as best as you can, whether the statements are true or false. + +a. There are real numbers $u$ and $v$ with the property that $u + v < u - v$. + +b. There is a real number $x$ such that $x^2 < x$. + +c. For every positive integer $n$, $n^2 \geq n$. + +d. For all real numbers $a$ and $b$, $|a + b| \leq |a| + |b|$. + +**Solution** + +a. There are real numbers $u$ and $v$ with the property that $u + v < u - v$. + +There are two distinct real numbers where the sum of those two numbers is less +than the difference of those two numbers. + +This is true if you consider our domain is all real numbers which include +negatives. For example: + +$$ 1 + (-1) = 0 $$ + +$$ 1 - (-1) = 2 $$ + +$$ 0 < 2 $$ + +b. There is a real number $x$ such that $x^2 < x$. + +There is a real number which is greater than it's square. + +This is true for any fraction/decimal. Consider: + +$$ \left(\frac{1}{4}\right)^2 = \frac{1}{16} $$ + +$$ \frac{1}{16} < \frac{1}{4} $$ + +c. For every positive integer $n$, $n^2 \geq n$. + +For all positive integers, an integer's square is always greater than or equal +to the integer. + +This is true. Starting at $1$ we get $1^2 \geq 1$, which is true, $2^2 \geq 2$ +is true, and so on. We're essentially multiplying each side of the inequality by +some positive integer, which we know from algebra does not change the direction +of the inequality, so this statement holds true. + +d. For all real numbers $a$ and $b$, $|a + b| \leq |a| + |b|$. + +For any two distinct real numbers, the absolute value of their sum is less than +or equal to the sum of the absolute values of each number. + +This is true, if both $a$ and $b$ are positive numbers or both $a$ and $b$ are +negative integers, then the two statements are equal. If either $a$ or $b$ is +negative and the other is positive, then the left statement will always be less +than the right hand statement. + +--- + +In each of 8-13, fill in the blanks to rewrite the given statement. + +8. For every object $J$, if $J$ is a square then $J$ has four sides. + +a. All squares ______. + +b. Every square ______. + +c. If an object is a square, then it ______. + +d. If $J$ ______, then $J$ ______. + +e. For every square $J$, ______. + +**Solution** + +a. All squares have four sides. + +b. Every square has four sides. + +c. If an object is a square, then it has four sides. + +d. If $J$ is a square, then $J$ has four sides. + +e. For every square $J$, $J$ has four sides. + +9. For every equation $E$, if $E$ is quadratic then $E$ has at most two real + solutions. + +a. All quadratic equations ______. + +b. Every quadratic equation ______. + +c. If an equation is quadratic, then it ______. + +d. If $E$ ______, then $E$ ______. + +e. For every quadratic equation $E$, ______. + +**Solution** + +a. All quadratic equations have at most two real solutions. + +b. Every quadratic equation has at most two real solutions. + +c. If an equation is quadratic, then it has at most two real solutions. + +d. If $E$ is a quadratic equation, then $E$ has at most two real solutions. + +e. For every quadratic equation $E$, $E$ has at most two real solutions. + +10. Every nonzero real number has a reciprocal. + +a. All nonzero real numbers ______. + +b. For every nonzero real number $r$, there is ______ for $r$. + +c. For every nonzero real number $r$, there is a real number $s$ such that +______. + +**Solution** + +a. All nonzero real numbers have reciprocals. + +b. For every nonzero real number $r$, there is a reciprocal for $r$. + +c. For every nonzero real number $r$, there is a real number $s$ such that $s$ +is a reciprocal of $r$. + +11. Every positive number has a positive square root. + +a. All positive numbers ______. + +b. For every positive number $e$, there is ______ for $e$. + +c. For every positive number $e$, there is a positive number $r$ such that +______. + +**Solution** + +a. All positive numbers have positive square roots. + +b. For every positive number $e$, there is a positive square root for $e$. + +c. For every positive number $e$, there is a positive number $r$ such that $r$ +is a positive square root for $e$. + +12. There is a real number whose product with every number leaves the number + unchanged. + +a. Some ______ has the property that its ______. + +b. There is a real number $r$ such that the product of $r$ ______. + +c. There is a real number $r$ with the property that for every real number $s$, +______. + +**Solution** + +a. Some real number has the property that its product with every number leaves +the number unchanged. + +b. There is a real number $r$ such that the product of $r$ with every number +leaves $r$ unchanged. + +c. There is a real number $r$ with the property that for every real number $s$, +such that $rs = s$. + +13. There is a real number whose product with every real number equals zero. + +a. Some _____ has the property that its ______. + +b. There is a real number $a$ such that the product of $a$ ______. + +c. There is a real number $a$ with the property that for every real number $b$, +______. + +**Solution** + +a. Some real number has the property that its product with every real number +equals zero. + +b. There is a real number $a$ such that the product of $a$ with every real +number equals zero. + +c. There is a real number $a$ with the property that for every real number $b$, +$ab = 0$. + +--- + +**Exercise Set 1.2** + +Page 37 + +1. Which of the following sets are equal? + +$$ A = \{a, b, c, d\} $$ + +$$ B = \{d, e, a, c\} $$ + +$$ C = \{d, b, a, c\} $$ + +$$ D = \{a, a, d, e, c, e\} $$ + +**Solution** + +$$ A = C $$ + +$$ B = D $$ + +2. Write in words how to read each of the following out loud. + +a. $\{x \in \mathbb{R}^+ | 0 < x < 1\}$ + +b. $\{x \in \mathbb{R} | x \leq 0 \text{ or } x \geq 1\}$ + +c. $\{n \in \mathbb{Z} | n \text{ is a factor of } 6\}$ + +d. $\{n \in \mathbb{Z}^+ | n \text{ is a factor of } 6\}$ + +**Solution** + +a. $\{x \in \mathbb{R}^+ | 0 < x < 1\}$ + +The set of all positive real numbers $x$ such that $x$ is greater than $0$ and +less than $1$. + +b. $\{x \in \mathbb{R} | x \leq 0 \text{ or } x \geq 1\}$ + +The set of all real numbers $x$ such that $x$ is less than or equal to $0$ or +$x$ is greater than or equal to $1$. + +c. $\{n \in \mathbb{Z} | n \text{ is a factor of } 6\}$ + +The set of all integers $n$ such that $n$ is a factor of $6$. + +d. $\{n \in \mathbb{Z}^+ | n \text{ is a factor of } 6\}$ + +The set of all positive integers $n$ such that $n$ is a factor of $6$. + +3. + +a. Is $4 = \{4\}$? + +b. How many elements are in the set $\{3, 4, 3, 5\}$? + +c. How many elements are in the set $\{1, \{1\}, \{1, \{1\}\}\}$ ? + +**Solution** + +a. Is $4 = \{4\}$? + +No, the symbol $4$, which represents the number four, does not equal the set +that contains an element that is the number $4$. + +b. How many elements are in the set $\{3, 4, 3, 5\}$? + +There are 3 elements in the set $\{3, 4, 3, 5\}$. Repeated elements are not +counted as more than 1 element in a set. + +c. How many elements are in the set $\{1, \{1\}, \{1, \{1\}\}\}$ ? + +There are three elements in the set, namely the symbol $1$, the set $\{1\}$, and +the set $\{1, \{1\}\}$. + +4. + +a. Is $2 \in \{2}$ ? + +b. How many elements are in the set $\{2, 2, 2, 2\}$ ? + +c. How many elements are in the set $\{0, \{0\}\}$ ? + +d. Is $\{0\} \in \{\{0\}, \{1\}\}$ ? + +e. Is $0 \in \{\{0\}, \{1\}\}$ ? + +**Solution** + +a. Is $2 \in \{2}$ ? + +No, the symbol $2$ which represents the number two, is not equal to the set +$\{2\}$, which is a set that contains the element $2$. + +b. How many elements are in the set $\{2, 2, 2, 2\}$ ? + +There is one element in the set $\{2, 2, 2, 2\}$, namely the element $2$. + +c. How many elements are in the set $\{0, \{0\}\}$ ? + +There are two elements in the set, namely the symbol $0$, and the set $\{0\}$. + +d. Is $\{0\} \in \{\{0\}, \{1\}\}$ ? + +Yes, the set of $\{0\}$ is in the set $\{\{0\}, \{1\}\}$, as the set contains +both the sets $\{0\}$ and $\{1\}$. + +e. Is $0 \in \{\{0\}, \{1\}\}$ ? + +No, the symbol $0$, representing the number zero, is not in the set, which holds +two sets with the symbols in them. + +5. Which of the following sets are equal? + +$$ +A = \{0, 1, 2\} \\ +B = \{x \in \mathbb{R} | -1 \leq x < 3\} \\ +C = \{x \in \mathbb{R} | -1 < x < 3\} \\ +D = \{x \in \mathbb{Z} | -1 < x < 3\} \\ +E = \{x \in \mathbb{Z}^+ | -1 < x < 3\} +$$ + +**Solution** + +None of these sets are equal. $A = E$ might have worked had $A$ not included +$0$, but $E$ essentially evaluates to $E = \{1, 2\}$, and does not include $0$. + +6. For each integer $n$, let $T_n = \{n, n^2\}$. How many elements are in each + of $T_2, T_{-3}, T_1$, and $T_0$? Justify your answers. + +**Solution** + +$$ T_2 = \{2, 2^2\} = \{2, 4\} \quad \text{ two elements } $$ + +$$ T_{-3} = \{-3, (-3)^2\} = \{-3, 9\} \quad \text{ two elements }$$ + +$$ T_1 = \{1, 1^2\} = \{1, 1\} = \{1\} \quad \text{ one element } $$ + +$$ T_0 = \{0, 0^2\} = \{0, 0\} = \{0\} \quad \text{ one element } $$ + +7. Use the set-roster notation to indicate the elements in each of the following + sets. + +a. $S = \{n \in \mathbb{Z} | n = (-1)^k \text{, for some integer } k\}$ + +b. $T = \{m \in \mathbb{Z}| m = 1 + (-1)^i \text{, for some integer } i\}$ + +c. $U = \{r \in \mathbb{Z} | 2 \leq r \leq -2\}$ + +d. $V = \{s \in \mathbb{Z} | s > 2 \text{ or }x < 3\}$ + +e. $W = \{t \in \mathbb{Z} | 1 < t < -3\}$ + +f. $X = \{u \in \mathbb{Z} | u \leq 4 \text{ or } u \geq 1\}$ + +**Solution** + +a. $S = \{n \in \mathbb{Z} | n = (-1)^k \text{, for some integer } k\}$ + +$$ \{-1, 1\} $$ + +b. $T = \{m \in \mathbb{Z}| m = 1 + (-1)^i \text{, for some integer } i\}$ + +$$ \{0, 2\} $$ + +c. $U = \{r \in \mathbb{Z} | 2 \leq r \leq -2\}$ + +$$ \emptyset $$ + +d. $V = \{s \in \mathbb{Z} | s > 2 \text{ or }x < 3\}$ + +$$ \mathbb{Z} $$ + +e. $W = \{t \in \mathbb{Z} | 1 < t < -3\}$ + +$$ \emptyset $$ + +f. $X = \{u \in \mathbb{Z} | u \leq 4 \text{ or } u \geq 1\}$ + +$$ \mathbb{Z}^+ $$ + +8. Let $A = \{c, d, f, g\}$, $B = \{f, j\}$, and $C = \{d, g\}$. Answer each of + the following questions. Give reasons for your answers. + +a. Is $B \subseteq A$? + +b. Is $C \subseteq A$? + +c. Is $C \subseteq C$? + +d. Is $C$ a proper subset of $A$? + +**Solution** + +a. Is $B \subseteq A$? + +No, because every element of $B$ must be an element of $A$ by definition of a +subset, but $j \in B$, but $j \notin A$. + +b. Is $C \subseteq A$? + +Yes, every element of $C$ is an element of $A$. + +c. Is $C \subseteq C$? + +Yes, every element of $C$ is an element of $C$. By implication, every set is a +subset of itself. + +d. Is $C$ a proper subset of $A$? + +Yes, $C \subset A$, but $C \neq A$. Every element of $C$ is an element of $A$, +but $C$ does not equal $A$, which is the definition of a proper subset. + +9. + +a. Is $3 \in \{1, 2, 3\}$? + +b. Is $1 \subseteq \{1}$? + +c. Is $\{2\} \in \{1, 2\}$? + +d. Is $\{3\} \in \{1, \{2\}, \{3\}\}$? + +e. Is $1 \in \{1\}$? + +f. Is $\{2\} \subseteq \{1, \{2\}, \{3\}\}$? + +g. Is $\{1\} \subseteq \{1, 2\}$? + +h. Is $1 \in \{\{1\}, 2\}$? + +i. Is $\{1\} \subseteq \{1, \{2\}\}$? + +j. Is $\{1\} \subseteq \{1\}$? + +**Solution** + +a. Is $3 \in \{1, 2, 3\}$? + +Yes, the symbol $3$, representing the number three, is in the set $\{1, 2, 3\}$. + +b. Is $1 \subseteq \{1}$? + +No, the number $1$ is not a set, and therefore cannot be a subset of $\{1\}$. + +c. Is $\{2\} \in \{1, 2\}$? + +No, the subset $\{2\}$ is not in the set $\{1, 2\}$, the number $2$ is in the +subset, but not the set $\{2\}$. + +d. Is $\{3\} \in \{1, \{2\}, \{3\}\}$? + +Yes, the set $\{3\}$ is an element of $\{1, \{2\}, \{3\}\}$. + +e. Is $1 \in \{1\}$? + +Yes, the number $1$ is in the set $\{1\}$. + +f. Is $\{2\} \subseteq \{1, \{2\}, \{3\}\}$? + +No, the set $\{2\}$ holds the element $2$, and $2$ is not an element in +$\{1, \{2\}, \{3\}\}$. + +g. Is $\{1\} \subseteq \{1, 2\}$? + +Yes, the set $\{\1}$ holds the element $1$, and $1$ is an element of $\{1, 2\}$. + +h. Is $1 \in \{\{1\}, 2\}$? + +No, the element $1$ is not in $\{\{1\}, 2\}$. + +i. Is $\{1\} \subseteq \{1, \{2\}\}$? + +Yes, the set $\{1\}$ holds the element $1$, which is an element of +$\{1, \{2\}\}$. + +j. Is $\{1\} \subseteq \{1\}$? + +Yes $\{1\}$ holds the element $1$, which is an element of $\{1\}$. They are +equal and it is implied that any set is a subset of itself. + +10. + +a. Is $((-2)^2, -2^2) = (-2^2, (-2)^2)$? + +b. Is $(5, -5) = (-5, 5)$? + +c. Is $(8 - 9, \sqrt[3]{-1}) = (-1, -1)$? + +d. Is $\left(\dfrac{-2}{-4}, (-2)^3\right) = \left(\dfrac{3}{6}, -8\right)$ + +**Solution** + +a. Is $((-2)^2, -2^2) = (-2^2, (-2)^2)$? + +$$ ((-2)^2, -2^2) = (4, -4) \neq (-4, 4) = (-2^2, (-2)^2) $$ + +So no, they are not equal. For ordered pair tuples to be equal, the order +matters and so each entry into the tuple must match the other for them to be +equal. + +b. Is $(5, -5) = (-5, 5)$? + +No, ordered pair tuples require that the entries be equal to each other _in +order_. + +c. Is $(8 - 9, \sqrt[3]{-1}) = (-1, -1)$? + +$$ (8 - 9, \sqrt[3]{-1}) = (-1, -1) = (-1, -1) $$ + +So yes, these two ordered pair tuples are equal. + +d. Is $\left(\dfrac{-2}{-4}, (-2)^3\right) = \left(\dfrac{3}{6}, -8\right)$ + +$$ \left(\dfrac{-2}{-4}, (-2)^3\right) = \left(\frac{1}{2}, -8\right) = \left(\frac{1}{2}, -8\right) = \left(\dfrac{3}{6}, -8\right) $$ + +So yes, these two ordered pair tuples are equal. + +11. Let $A = \{w, x, y, z\}$ and $B = \{a, b\}$. Use set-roster notation to + write each of the following sets, and indicate the number of elements that + are in each set. + +a. $A \times B$ + +b. $B \times A$ + +c. $A \times A$ + +d. $B \times B$ + +**Solution** + +a. $A \times B$ + +$$ A \times B = \{(w, a), (w, b), (x, a), (x, b), (y, a), (y, b), (z, a), (z, b)\} $$ + +There are 8 elements in $A \times B$. + +b. $B \times A$ + +$$ B \times A = \{(a, w), (b, w), (a, x), (b, x), (a, y), (b, y), (a, z), (b, z)\} $$ + +There are 8 elements in $B \times A$. + +c. $A \times A$ + +$$ A \times A = \{(w, w), (w, x), (w, y), (w, z), (x, w), (x, x), (x, y), (x, z), (y, w), (y, x), (y, y), (y, z), (z, w), (z, x), (z, y), (z, z)\} $$ + +There are 16 elements in $A \times A$. + +d. $B \times B$ + +$$ B \times B = \{(a, a), (a, b), (b, a), (b, b)\} $$ + +There are 4 elements in $B \times B$. + +12. Let $S = \{2, 4, 6\}$ and $T = \{1, 3, 5\}$. Use the set-roster notation to + write each of the following sets, and indicate the number of elements that + are in each set. + +a. $S \times T$ + +b. $T \times S$ + +c. $S \times S$ + +d. $T \times T$ + +**Solution** + +a. $S \times T$ + +$$ S \times T = \{(2, 1), (2, 3), (2, 5), (4, 1), (4, 3), (4, 5), (6, 1), (6, 3), (6, 5)\} $$ + +There are 9 elements in $S \times T$. + +b. $T \times S$ + +$$ T \times S = \{(1, 2), (1, 4), (1, 6), (3, 2), (3, 4), (3, 6), (5, 2), (5, 4), (5, 6)\} $$ + +There are 9 elements in $T \times S$. + +c. $S \times S$ + +$$ S \times S = \{(2, 2), (2, 4), (2, 6), (4, 2), (4, 4), (4, 6), (6, 2), (6, 4), (6, 6)\} $$ + +There are 9 elements in $S \times S$. + +d. $T \times T$ + +$$ T \times T = \{(1, 1), (1, 3), (1, 5), (3, 1), (3, 3), (3, 5), (5, 1), (5, 3), (5, 5)\} $$ + +There are 9 elements in $T \times T$. + +13. Let $A = \{1, 2, 3\}$, $B = \{u\}$, and $C = \{m, n\}$. Find each of the + following sets. + +a. $A \times (B \times C)$ + +b. $(A \times B) \times C$ + +c. $A \times B \times C$ + +**Solution** + +a. $A \times (B \times C)$ + +$$ B \times C = \{(u, m), (u, n)\} $$ + +$$ A \times (B \times C) = \{(1, (u, m)), (1, (u, n)), (2, (u, m)), (2, (u, n)), (3, (u, m)), (3, (u, n))\} $$ + +b. $(A \times B) \times C$ + +$$ A \times B = \{(1, u), (2, u), (3, u)\} $$ + +$$ (A \times B) \times C = \{((1, u), m), ((1, u), n), ((2, u), m), ((2, u), n), ((3, u), m), ((3, u), n)\} $$ + +c. $A \times B \times C$ + +$$ A \times B \times C = \{(1, u, m), (1, u, n), (2, u, m), (2, u, n), (3, u, m), (3, u, n)\} $$ + +14. Let $R = \{a\}$, $S = \{x, y\}$, and $T = \{p, q, r\}$. Find each of the + following sets. + +a. $R \times (S \times T)$ + +$$ S \times T = \{(x, p), (x, q), (x, r), (y, p), (y, q), (y, r)\} $$ + +$$ R \times (S \times T) = \{(a, (x, p)), (a, (x, q)), (a, (x, r)), (a, (y, p)), (a, (y, q)), (a, (y, r))\} $$ + +b. $(R \times S) \times T$ + +$$ R \times S = \{(a, x), (a, y)\} $$ + +$$ (R \times S) \times T = \{((a, x), p), ((a, x), q), ((a, x), r), ((a, y), p), ((a, y), q), ((a, y), r)\} $$ + +c. $R \times S \times T$ + +**Solution** + +$$ R \times S \times T = \{(a, x, p), (a, x, q), (a, x, r), (a, y, p), (a, y, q), (a, y, r)\} $$ + +a. $R \times (S \times T)$ + +b. $(R \times S) \times T$ + +c. $R \times S \times T$ + +15. Let $S = \{0, 1\}$. List all the strings of length 4 over $S$ that contain + three or more $0$'s. + +**Solution** + +0000, 0001, 0010, 0100, 1000 + +16. Let $T = \{x, y\}$. List all the strings of length 5 over $T$ that have + exactly one $y$. + +**Solution** + +xxxxy, xxxyx, xxyxx, xyxxx, yxxxx diff --git a/chapter_1/notes.md b/chapter_1/notes.md new file mode 100644 index 0000000..807fb9b --- /dev/null +++ b/chapter_1/notes.md @@ -0,0 +1,152 @@ +Page 25 + +A **universal statement** says that a certain property is true for all elements +in a set. (For example: _All positive numbers are greater than zero_.) + +A **conditional statement** says that if one thing is true then some other thing +also has to be true. (For example: _If 378 is divisible by 18, then 378 is +divisible by 6_.) + +Given a property that may or may not be true, an **existential statement** says +that there is at least one thing for which the property is true. (For example: +_There is a prime number that is even_.) + +--- + +Page 30 + +**Set Roster Notation** + +If $S$ is a set, the notation $x \in S$ means that $x$ is an element of $S$. The +notation $x \notin S$ means that $x$ is not an element of $S$. A set may be +specified using the **set-roster notation** by writing all of its elements +between braces. For example, $\{1, 2, 3\}$ denotes the set whose elements are +$1$, $2$, and $3$. A variation of the notation is sometimes used to describe a +very large set, as when we write $\{1, 2, 3, \dots, 100\}$ to refer to the set +of all integers from $1$ to $100$. A similar notation can also describe an +infinite set, as when we write $\{1, 2, 3, \dots\}$ to refer to the set of all +positive integers. (The symbol $\dots$ is called an **ellipsis** and is read +"and so forth.") + +The **axiom of extension** says that a set is completely determined by what its +elements are - not the order in which they might be listed or the fact that some +elements might be listed more than once. + +--- + +Page 30 + +| Symbol | Set | +| ---------- | --------------------------------------------------------- | +| \mathbb{R} | the set of all real numbers | +| \mathbb{Z} | the set of all integers | +| \mathbb{Q} | the set of all rational numbers, or quotients of integers | + +--- + +Page 31 + +**Set-Builder Notation** + +Let $S$ denote a set and let $P(x)$ be a property that elements of $S$ may or +may not satisfy. We may define a new set to be **the set of all elements $x$ in +$S$ such that $P(x)$ is true**. We denote this set as follows: + +$$ \{x \in S | P(x)\} $$ + +Where $x$ is "the set of all" and $|$ is "such that." + +--- + +Page 32 + +**Definition** + +If $A$ and $B$ are sets, then $A$ is called a **subset** of $B$, written +$A \subseteq B$, if and only if, every element of $A$ is also an element of $B$. + +Symbolically: + +$A \subseteq B$ means that for every element $x$, if $x \in A$ then $x \in B$. + +The phrases $A$ _is contained in_ $B$ and $B$ _contains_ $A$ are alternative +ways of saying that $A$ is a subset of $B$. + +It follows from the definition of subset that for a set $A$ not to be a subset +of a set $B$ means that there is at least one element of $A$ that is not an +element of $B$. Symbolically: + +$A \nsubseteq B$ means that there is at least one element $x$ such that +$x \in A$ and $x \notin B$. + +**Definition** + +Let $A$ and $B$ be sets. $A$ is a **proper subset** of $B$ if, and only if, +every element of $A$ is in $B$ but there is at least one element of $B$ that is +not in $A$. + +--- + +Page 33 + +**Notation** + +Given elements $a$ and $b$, the symbol $(a, b)$ denotes the **ordered pair** +consisting of $a$ and $b$ together with the specification that $a$ is the first +element of the pair and $b$ is the second element. Two ordered pairs $(a, b)$ +and $(c, d)$ are equal if, and only if, $a = c$ and $b = d$. Symbolically: + +$(a, b) = (c, d)$ means that $a = c$ and $b = d$. + +--- + +Page 34 + +**Definition** + +Let $n$ be a positive integer and let $x_1, x_2, \dots, x_n$ be (not necessarily +distinct) elements. The **ordered $n$-tuple, $(x_1, x_2, \dots, x_n)$**, +consists of $x_1$, $x_2$, $\dots$, $x_n$ together with the ordering: first +$x_1$, then $x_2$, and so forth up to $x_n$. An ordered 2-tuple is called an +**ordered pair**, and an ordered 3-tuple is called an **ordered triple.** + +Two ordered $n$-tuples $(x_1, x_2, \dots, x_n)$ and $(y_1, y_2, \dots, y_n)$ are +**equal** if, and only if, $x_1 = y^1$, $x^2 = y^2$, $\dots$, and $x_n = y_n$. + +Symbolically: + +$$ (x_1, x_2, \dots x_n) = (y_1, y_2, \dots, y_n) \leftrightarrow x_1 = y_1, x^2 = y_2, \dots , x_n = y_n $$ + +--- + +Page 35 + +**Definition** + +Given sets $A_1, A_2, \dots, A_n$, the **Cartesian product** of +$A_1, A_2, \dots, A_n$ denoted $A_1 \times A_2 \times \dots \times A_n$, is the +set of all ordered $n$-tuples $(a_1, a_2, \dots, a_n)$ where +$a_1 \in A_1, a_2 \in A_2, \dots , a_n \in A_n$. + +Symbolically: + +$$ A_1 \times A_2 \times \dots \times A_n = \{(a_1, a_2, \dots, a_n) | a_1 \in A_1, a_2 \in A_2, \dots , a_n \in A_n\} $$ + +In particular, + +$$ A_1 \times A_2 = \{(a_1, a_2) | a_1 \in A_1 \text{ and } a_2 \in A_2\} $$ + +is the Cartesian product of $A_1$ and $A_2$. + +--- + +Page 36 + +**Definition** + +Let $n$ be a positive integer. Given a finite set $A$, a **string of length $n$ +over $A$** is an ordered $n$-tuple of elements of $A$ written without +parentheses or commas. The elements of $A$ are called the **characters** of the +string. The **null string** over $A$ is defined to be the "string" with no +characters. It is often denoted $\lambda$ and is said to have length $0$. If +$A = \{0, 1\}$, then a string over $A$ is called a **bit string**. diff --git a/chapter_1/test_yourself.md b/chapter_1/test_yourself.md new file mode 100644 index 0000000..55efaf4 --- /dev/null +++ b/chapter_1/test_yourself.md @@ -0,0 +1,83 @@ +**Test Yourself** + +Page 28 + +1. A universal statement asserts that a certain property is _______ for _______. + +2. A conditional statement asserts that if one thing _______ then some other + thing _______. + +3. Given a property that may or may not be true, an existential statement + asserts that _______ for which the property is true. + +**Solutions**: + +1. true, for all elements of a set. + +2. is true, also has to be true. + +3. there is at least one thing + +--- + +**Test Yourself** + +Page 37 + +1. When the elements of a set are given using the set-roster notation, the order + in which they are listed _______. + +**Solution** + +does not matter. + +2. The symbol $\mathbb{R}$ denotes _______. + +**Solution** + +The set of all real numbers. + +3. The symbol $\mathbb{Z}$ denotes _______. + +**Solution** + +The set of all integers. + +4. The symbol $\mathbb{Q}$ denotes _______. + +**Solution** + +The set of all rational numbers. + +5. The notation $\{x | P(x)\}$ is read _______. + +**Solution** + +The set of all $x$ such that $P(x)$ is true. + +6. For a set $A$ to be a subset of a set $B$ means that _______. + +**Solution** + +Every element in $A$ is an element in $B$. + +7. Given sets $A$ and $B$, the Cartesian product $A \times B$ is _______. + +**Solution** + +The set of all ordered pairs $(a, b)$ where $a \in A$ and $b \in B$. + +8. Given sets $A$, $B$, and $C$, the Cartesian product $A \times B \times C$ is + _______. + +The set of all ordered triples, $(a, b, c)$ where $a \in A$ and $b \in B$ and +$c \in C$. + +**Solution** + +9. A string of length $n$ over a set $S$ is an ordered $n$-tuple of elements + $S$, written without _______ or _______. + +**Solution** + +parentheses; commas diff --git a/leftoff.txt b/leftoff.txt index 573541a..e522732 100644 --- a/leftoff.txt +++ b/leftoff.txt @@ -1 +1 @@ -0 +38