# 3.1 Exponents and roots

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This module is from Fundamentals of Mathematics by Denny Burzynski and Wade Ellis, Jr. This module discusses exponents and roots. By the end of the module students should be able to understand and be able to read exponential notation, understand the concept of root and be able to read root notation, and use a calculator having the ${y}^{x}$ key to determine a root.

## Section overview

• Exponential Notation
• Reading Exponential Notation
• Roots
• Reading Root Notation
• Calculators

## Exponential notation

We have noted that multiplication is a description of repeated addition. Exponen­tial notation is a description of repeated multiplication.

Suppose we have the repeated multiplication

$8\cdot 8\cdot 8\cdot 8\cdot 8$

## Exponent

The factor 8 is repeated 5 times. Exponential notation uses a superscript for the number of times the factor is repeated. The superscript is placed on the repeated factor, ${8}^{5}$ , in this case. The superscript is called an exponent .

## The function of an exponent

An exponent records the number of identical factors that are repeated in a multiplication.

## Sample set a

Write the following multiplication using exponents.

$3\cdot 3$ . Since the factor 3 appears 2 times, we record this as

${3}^{2}$

$\text{62}\cdot \text{62}\cdot \text{62}\cdot \text{62}\cdot \text{62}\cdot \text{62}\cdot \text{62}\cdot \text{62}\cdot \text{62}$ . Since the factor 62 appears 9 times, we record this as

${\text{62}}^{9}$

Expand (write without exponents) each number.

${\text{12}}^{4}$ . The exponent 4 is recording 4 factors of 12 in a multiplication. Thus,

${\text{12}}^{4}=\text{12}\cdot \text{12}\cdot \text{12}\cdot \text{12}$

${\text{706}}^{3}$ . The exponent 3 is recording 3 factors of 706 in a multiplication. Thus,

${\text{706}}^{3}=\text{706}\cdot \text{706}\cdot \text{706}$

## Practice set a

Write the following using exponents.

$\text{37}\cdot \text{37}$

${\text{37}}^{2}$

$\text{16}\cdot \text{16}\cdot \text{16}\cdot \text{16}\cdot \text{16}$

${\text{16}}^{5}$

$9\cdot 9\cdot 9\cdot 9\cdot 9\cdot 9\cdot 9\cdot 9\cdot 9\cdot 9$

${9}^{\text{10}}$

Write each number without exponents.

${\text{85}}^{3}$

$\text{85}\cdot \text{85}\cdot \text{85}$

${4}^{7}$

$4\cdot 4\cdot 4\cdot 4\cdot 4\cdot 4\cdot 4$

$1,{\text{739}}^{2}$

$1,\text{739}\cdot 1,\text{739}$

## Reading exponential notation

In a number such as ${8}^{5}$ ,

## Base

8 is called the base .

## Exponent, power

5 is called the exponent , or power . ${8}^{5}$ is read as "eight to the fifth power," or more simply as "eight to the fifth," or "the fifth power of eight."

## Squared

When a whole number is raised to the second power, it is said to be squared . The number ${5}^{2}$ can be read as

5 to the second power, or
5 to the second, or
5 squared.

## Cubed

When a whole number is raised to the third power, it is said to be cubed . The number ${5}^{3}$ can be read as

5 to the third power, or
5 to the third, or
5 cubed.

When a whole number is raised to the power of 4 or higher, we simply say that that number is raised to that particular power. The number ${5}^{8}$ can be read as

5 to the eighth power, or just
5 to the eighth.

## Roots

In the English language, the word "root" can mean a source of something. In mathematical terms, the word "root" is used to indicate that one number is the source of another number through repeated multiplication.

## Square root

We know that $\text{49}={7}^{2}$ , that is, $\text{49}=7\cdot 7$ . Through repeated multiplication, 7 is the source of 49. Thus, 7 is a root of 49. Since two 7's must be multiplied together to produce 49, the 7 is called the second or square root of 49.

## Cube root

We know that $8={2}^{3}$ , that is, $8=2\cdot 2\cdot 2$ . Through repeated multiplication, 2 is the source of 8. Thus, 2 is a root of 8. Since three 2's must be multiplied together to produce 8, 2 is called the third or cube root of 8.

#### Questions & Answers

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in general
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Source:  OpenStax, Fundamentals of mathematics. OpenStax CNX. Aug 18, 2010 Download for free at http://cnx.org/content/col10615/1.4
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