In this section students will:
It is often said that mathematics is the language of science. If this is true, then an essential part of the language of mathematics is numbers. The earliest use of numbers occurred 100 centuries ago in the Middle East to count, or enumerate items. Farmers, cattlemen, and tradesmen used tokens, stones, or markers to signify a single quantity—a sheaf of grain, a head of livestock, or a fixed length of cloth, for example. Doing so made commerce possible, leading to improved communications and the spread of civilization.
Three to four thousand years ago, Egyptians introduced fractions. They first used them to show reciprocals. Later, they used them to represent the amount when a quantity was divided into equal parts.
But what if there were no cattle to trade or an entire crop of grain was lost in a flood? How could someone indicate the existence of nothing? From earliest times, people had thought of a “base state” while counting and used various symbols to represent this null condition. However, it was not until about the fifth century A.D. in India that zero was added to the number system and used as a numeral in calculations.
Clearly, there was also a need for numbers to represent loss or debt. In India, in the seventh century A.D., negative numbers were used as solutions to mathematical equations and commercial debts. The opposites of the counting numbers expanded the number system even further.
Because of the evolution of the number system, we can now perform complex calculations using these and other categories of real numbers. In this section, we will explore sets of numbers, calculations with different kinds of numbers, and the use of numbers in expressions.
The numbers we use for counting, or enumerating items, are the natural numbers: 1, 2, 3, 4, 5, and so on. We describe them in set notation as
where the ellipsis (…) indicates that the numbers continue to infinity. The natural numbers are, of course, also called the counting numbers. Any time we enumerate the members of a team, count the coins in a collection, or tally the trees in a grove, we are using the set of natural numbers. The set of whole numbers is the set of natural numbers plus zero:
The set of integers adds the opposites of the natural numbers to the set of whole numbers:
It is useful to note that the set of integers is made up of three distinct subsets: negative integers, zero, and positive integers. In this sense, the positive integers are just the natural numbers. Another way to think about it is that the natural numbers are a subset of the integers.
The set of rational numbers is written as
Notice from the definition that rational numbers are fractions (or quotients) containing integers in both the numerator and the denominator, and the denominator is never 0. We can also see that every natural number, whole number, and integer is a rational number with a denominator of 1.
Because they are fractions, any rational number can also be expressed in decimal form. Any rational number can be represented as either:
or
We use a line drawn over the repeating block of numbers instead of writing the group multiple times.
Write each of the following as a rational number.
Write a fraction with the integer in the numerator and 1 in the denominator.
Write each of the following as a rational number.
Write each of the following rational numbers as either a terminating or repeating decimal.
Write each fraction as a decimal by dividing the numerator by the denominator.
a repeating decimal
(or 3.0), a terminating decimal
a terminating decimal
Write each of the following rational numbers as either a terminating or repeating decimal.
repeating;
At some point in the ancient past, someone discovered that not all numbers are rational numbers. A builder, for instance, may have found that the diagonal of a square with unit sides was not 2 or even
but was something else. Or a garment maker might have observed that the ratio of the circumference to the diameter of a roll of cloth was a little bit more than 3, but still not a rational number. Such numbers are said to be irrational because they cannot be written as fractions. These numbers make up the set of irrational numbers. Irrational numbers cannot be expressed as a fraction of two integers. It is impossible to describe this set of numbers by a single rule except to say that a number is irrational if it is not rational. So we write this as shown.
Determine whether each of the following numbers is rational or irrational. If it is rational, determine whether it is a terminating or repeating decimal.
This can be simplified as
Therefore,
is rational.
Because it is a fraction,
is a rational number. Next, simplify and divide.
So,
is rational and a repeating decimal.
This cannot be simplified any further. Therefore,
is an irrational number.
Because it is a fraction,
is a rational number. Simplify and divide.
So,
is rational and a terminating decimal.
is not a terminating decimal. Also note that there is no repeating pattern because the group of 3s increases each time. Therefore it is neither a terminating nor a repeating decimal and, hence, not a rational number. It is an irrational number.
Determine whether each of the following numbers is rational or irrational. If it is rational, determine whether it is a terminating or repeating decimal.
Given any number n, we know that n is either rational or irrational. It cannot be both. The sets of rational and irrational numbers together make up the set of real numbers. As we saw with integers, the real numbers can be divided into three subsets: negative real numbers, zero, and positive real numbers. Each subset includes fractions, decimals, and irrational numbers according to their algebraic sign (+ or –). Zero is considered neither positive nor negative.
The real numbers can be visualized on a horizontal number line with an arbitrary point chosen as 0, with negative numbers to the left of 0 and positive numbers to the right of 0. A fixed unit distance is then used to mark off each integer (or other basic value) on either side of 0. Any real number corresponds to a unique position on the number line.The converse is also true: Each location on the number line corresponds to exactly one real number. This is known as a one-to-one correspondence. We refer to this as the real number line as shown in [link].
Classify each number as either positive or negative and as either rational or irrational. Does the number lie to the left or the right of 0 on the number line?
is negative and rational. It lies to the left of 0 on the number line.
is positive and irrational. It lies to the right of 0.
is negative and rational. It lies to the left of 0.
is negative and irrational. It lies to the left of 0.
is a repeating decimal so it is rational and positive. It lies to the right of 0.
Classify each number as either positive or negative and as either rational or irrational. Does the number lie to the left or the right of 0 on the number line?
Beginning with the natural numbers, we have expanded each set to form a larger set, meaning that there is a subset relationship between the sets of numbers we have encountered so far. These relationships become more obvious when seen as a diagram, such as [link].
The set of natural numbers includes the numbers used for counting:
The set of whole numbers is the set of natural numbers plus zero:
The set of integers adds the negative natural numbers to the set of whole numbers:
The set of rational numbers includes fractions written as
The set of irrational numbers is the set of numbers that are not rational, are nonrepeating, and are nonterminating:
Classify each number as being a natural number (N), whole number (W), integer (I), rational number (Q), and/or irrational number (Q′).
N | W | I | Q | Q′ | |
---|---|---|---|---|---|
a. |
X | X | X | X | |
b. |
X | ||||
c. |
X | |||||
d. –6 | X | X | |||
e. 3.2121121112… | X |
Classify each number as being a natural number (N), whole number (W), integer (I), rational number (Q), and/or irrational number (Q′).
N | W | I | Q | Q’ | |
---|---|---|---|---|---|
a. |
X | X | ||||
b. 0 | X | X | X | ||
c. |
X | X | X | X | |
d. |
X | |||||
e. 4.763763763… | X |
When we multiply a number by itself, we square it or raise it to a power of 2. For example,
We can raise any number to any power. In general, the exponential notation
means that the number or variable
is used as a factor
times.
In this notation,
is read as the nth power of
where
is called the base and
is called the exponent. A term in exponential notation may be part of a mathematical expression, which is a combination of numbers and operations. For example,
is a mathematical expression.
To evaluate a mathematical expression, we perform the various operations. However, we do not perform them in any random order. We use the order of operations. This is a sequence of rules for evaluating such expressions.
Recall that in mathematics we use parentheses ( ), brackets [ ], and braces { } to group numbers and expressions so that anything appearing within the symbols is treated as a unit. Additionally, fraction bars, radicals, and absolute value bars are treated as grouping symbols. When evaluating a mathematical expression, begin by simplifying expressions within grouping symbols.
The next step is to address any exponents or radicals. Afterward, perform multiplication and division from left to right and finally addition and subtraction from left to right.
Let’s take a look at the expression provided.
There are no grouping symbols, so we move on to exponents or radicals. The number 4 is raised to a power of 2, so simplify
as 16.
Next, perform multiplication or division, left to right.
Lastly, perform addition or subtraction, left to right.
Therefore,
For some complicated expressions, several passes through the order of operations will be needed. For instance, there may be a radical expression inside parentheses that must be simplified before the parentheses are evaluated. Following the order of operations ensures that anyone simplifying the same mathematical expression will get the same result.
Operations in mathematical expressions must be evaluated in a systematic order, which can be simplified using the acronym PEMDAS:
P(arentheses)* * *
E(xponents)* * *
M(ultiplication) and D(ivision)* * *
A(ddition) and S(ubtraction)
Given a mathematical expression, simplify it using the order of operations.
Use the order of operations to evaluate each of the following expressions.
Note that in the first step, the radical is treated as a grouping symbol, like parentheses. Also, in the third step, the fraction bar is considered a grouping symbol so the numerator is considered to be grouped.
In this example, the fraction bar separates the numerator and denominator, which we simplify separately until the last step.
Use the order of operations to evaluate each of the following expressions.
For some activities we perform, the order of certain operations does not matter, but the order of other operations does. For example, it does not make a difference if we put on the right shoe before the left or vice-versa. However, it does matter whether we put on shoes or socks first. The same thing is true for operations in mathematics.
The commutative property of addition states that numbers may be added in any order without affecting the sum.
We can better see this relationship when using real numbers.
Similarly, the commutative property of multiplication states that numbers may be multiplied in any order without affecting the product.
Again, consider an example with real numbers.
It is important to note that neither subtraction nor division is commutative. For example,
is not the same as
Similarly,
The associative property of multiplication tells us that it does not matter how we group numbers when multiplying. We can move the grouping symbols to make the calculation easier, and the product remains the same.
Consider this example.
The associative property of addition tells us that numbers may be grouped differently without affecting the sum.
This property can be especially helpful when dealing with negative integers. Consider this example.
Are subtraction and division associative? Review these examples.
As we can see, neither subtraction nor division is associative.
The distributive property states that the product of a factor times a sum is the sum of the factor times each term in the sum.
This property combines both addition and multiplication (and is the only property to do so). Let us consider an example.
Note that 4 is outside the grouping symbols, so we distribute the 4 by multiplying it by 12, multiplying it by –7, and adding the products.
To be more precise when describing this property, we say that multiplication distributes over addition. The reverse is not true, as we can see in this example.
A special case of the distributive property occurs when a sum of terms is subtracted.
For example, consider the difference
We can rewrite the difference of the two terms 12 and
by turning the subtraction expression into addition of the opposite. So instead of subtracting
we add the opposite.
Now, distribute
and simplify the result.
This seems like a lot of trouble for a simple sum, but it illustrates a powerful result that will be useful once we introduce algebraic terms. To subtract a sum of terms, change the sign of each term and add the results. With this in mind, we can rewrite the last example.
The identity property of addition states that there is a unique number, called the additive identity (0) that, when added to a number, results in the original number.
The identity property of multiplication states that there is a unique number, called the multiplicative identity (1) that, when multiplied by a number, results in the original number.
For example, we have
and
There are no exceptions for these properties; they work for every real number, including 0 and 1.
The inverse property of addition states that, for every real number a, there is a unique number, called the additive inverse (or opposite), denoted−a, that, when added to the original number, results in the additive identity, 0.
For example, if
the additive inverse is 8, since
The inverse property of multiplication holds for all real numbers except 0 because the reciprocal of 0 is not defined. The property states that, for every real number a, there is a unique number, called the multiplicative inverse (or reciprocal), denoted
that, when multiplied by the original number, results in the multiplicative identity, 1.
For example, if
the reciprocal, denoted
is
because
The following properties hold for real numbers a, b, and c.
Addition | Multiplication | |
Commutative Property | ||
Associative Property | ||
Distributive Property | ||
Identity Property | There exists a unique real number called the additive identity, 0, such that, for any real number a | There exists a unique real number called the multiplicative identity, 1, such that, for any real number a |
Inverse Property | Every real number a has an additive inverse, or opposite, denoted –a, such that | Every nonzero real number a has a multiplicative inverse, or reciprocal, denotedsuch that |
Use the properties of real numbers to rewrite and simplify each expression. State which properties apply.
Use the properties of real numbers to rewrite and simplify each expression. State which properties apply.
commutative property of addition, associative property of addition, inverse property of addition, identity property of addition;
So far, the mathematical expressions we have seen have involved real numbers only. In mathematics, we may see expressions such as
or
In the expression
5 is called a constant because it does not vary and x is called a variable because it does. (In naming the variable, ignore any exponents or radicals containing the variable.) An algebraic expression is a collection of constants and variables joined together by the algebraic operations of addition, subtraction, multiplication, and division.
We have already seen some real number examples of exponential notation, a shorthand method of writing products of the same factor. When variables are used, the constants and variables are treated the same way.
In each case, the exponent tells us how many factors of the base to use, whether the base consists of constants or variables.
Any variable in an algebraic expression may take on or be assigned different values. When that happens, the value of the algebraic expression changes. To evaluate an algebraic expression means to determine the value of the expression for a given value of each variable in the expression. Replace each variable in the expression with the given value, then simplify the resulting expression using the order of operations. If the algebraic expression contains more than one variable, replace each variable with its assigned value and simplify the expression as before.
List the constants and variables for each algebraic expression.
Constants | Variables | |
---|---|---|
a. x + 5 | 5 | x |
b. |
c. |
2 |
List the constants and variables for each algebraic expression.
Constants | Variables | |
---|---|---|
a. | ||
b. 2(L + W) | 2 | L, W |
c. | 4 |
Evaluate the expression
for each value for x.
for
for
Evaluate the expression
for each value for y.
Evaluate each expression for the given values.
for
for
for
for
for
for
and –8 for
and 3 for
Evaluate each expression for the given values.
for
for
for
for
for
;
An equation is a mathematical statement indicating that two expressions are equal. The expressions can be numerical or algebraic. The equation is not inherently true or false, but only a proposition. The values that make the equation true, the solutions, are found using the properties of real numbers and other results. For example, the equation
has the unique solution of 3
because when we substitute 3 for
in the equation, we obtain the true statement
A formula is an equation expressing a relationship between constant and variable quantities. Very often, the equation is a means of finding the value of one quantity (often a single variable) in terms of another or other quantities. One of the most common examples is the formula for finding the area
of a circle in terms of the radius
of the circle:
For any value of
the area
can be found by evaluating the expression
A right circular cylinder with radius
and height
has the surface area
(in square units) given by the formula
See [link]. Find the surface area of a cylinder with radius 6 in. and height 9 in. Leave the answer in terms of
Evaluate the expression
for
and
The surface area is
square inches.
A photograph with length L and width W is placed in a matte of width 8 centimeters (cm). The area of the matte (in square centimeters, or cm2) is found to be
See [link]. Find the area of a matte for a photograph with length 32 cm and width 24 cm.
1,152 cm2
Sometimes we can simplify an algebraic expression to make it easier to evaluate or to use in some other way. To do so, we use the properties of real numbers. We can use the same properties in formulas because they contain algebraic expressions.
Simplify each algebraic expression.
Simplify each algebraic expression.
A rectangle with length
and width
has a perimeter
given by
Simplify this expression.
If the amount
is deposited into an account paying simple interest
for time
the total value of the deposit
is given by
Simplify the expression. (This formula will be explored in more detail later in the course.)
Access these online resources for additional instruction and practice with real numbers.
Is
an example of a rational terminating, rational repeating, or irrational number? Tell why it fits that category.
irrational number. The square root of two does not terminate, and it does not repeat a pattern. It cannot be written as a quotient of two integers, so it is irrational.
What is the order of operations? What acronym is used to describe the order of operations, and what does it stand for?
What do the Associative Properties allow us to do when following the order of operations? Explain your answer.
The Associative Properties state that the sum or product of multiple numbers can be grouped differently without affecting the result. This is because the same operation is performed (either addition or subtraction), so the terms can be re-ordered.
For the following exercises, simplify the given expression.
9
-2
4
0
9
25
17
4
For the following exercises, solve for the variable.
2
2
For the following exercises, simplify the expression.
For the following exercises, consider this scenario: Fred earns $40 mowing lawns. He spends $10 on mp3s, puts half of what is left in a savings account, and gets another $5 for washing his neighbor’s car.
Write the expression that represents the number of dollars Fred keeps (and does not put in his savings account). Remember the order of operations.
How much money does Fred keep?
For the following exercises, solve the given problem.
According to the U.S. Mint, the diameter of a quarter is 0.955 inches. The circumference of the quarter would be the diameter multiplied by
Is the circumference of a quarter a whole number, a rational number, or an irrational number?
irrational number
Jessica and her roommate, Adriana, have decided to share a change jar for joint expenses. Jessica put her loose change in the jar first, and then Adriana put her change in the jar. We know that it does not matter in which order the change was added to the jar. What property of addition describes this fact?
For the following exercises, consider this scenario: There is a mound of
pounds of gravel in a quarry. Throughout the day, 400 pounds of gravel is added to the mound. Two orders of 600 pounds are sold and the gravel is removed from the mound. At the end of the day, the mound has 1,200 pounds of gravel.
Write the equation that describes the situation.
Solve for g.
For the following exercise, solve the given problem.
Ramon runs the marketing department at his company. His department gets a budget every year, and every year, he must spend the entire budget without going over. If he spends less than the budget, then his department gets a smaller budget the following year. At the beginning of this year, Ramon got $2.5 million for the annual marketing budget. He must spend the budget such that
What property of addition tells us what the value of x must be?
inverse property of addition
For the following exercises, use a graphing calculator to solve for x. Round the answers to the nearest hundredth.
68.4
If a whole number is not a natural number, what must the number be?
Determine whether the statement is true or false: The multiplicative inverse of a rational number is also rational.
true
Determine whether the statement is true or false: The product of a rational and irrational number is always irrational.
Determine whether the simplified expression is rational or irrational:
irrational
Determine whether the simplified expression is rational or irrational:
The division of two whole numbers will always result in what type of number?
rational
What property of real numbers would simplify the following expression:
there is a unique number, called the additive inverse (or opposite), denoted
which, when added to the original number, results in the additive identity, 0; in symbols,
there is a unique number, called the multiplicative inverse (or reciprocal), denoted
which, when multiplied by the original number, results in the multiplicative identity, 1; in symbols,
where
and
are integers and
Any rational number may be written as a fraction or a terminating or repeating decimal.
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