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Working with Exponents Study Guide

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Updated on Aug 24, 2011

Find practice problems and solutions for these concepts at Working with Exponents Practice Problems.

This lesson shows you how to add, subtract, multiply, and divide expressions with exponents. You will also learn how to raise expressions to a power.

What Is an Exponent?

An exponent tells you how many times a factor is multiplied. An exponent appears as a raised number that is smaller in size than the other numbers on the page. For example, in the expression 43, the three is the exponent. The expression 43 shows that four is a factor three times. That means four times four times four. Here are examples of exponents and what they mean:

52 = 5 · 5

23= 2 · 2 · 2

a2 = a · a

2x3y2 = 2 · x · x · x · y · y

A googol is a 1 followed by 100 zeros. Using exponents, this is written as 10100. The term googol was coined by the eight-year-old nephew of American mathematician Edward Kasner in 1938. Kasner asked his nephew what he would name a really large number, and "googol" was the boy's response.

Adding and Subtracting with Exponents

In previous lessons, when you combined similar terms, you added the numbers in front of the variables (coefficients) and left the variables the same. Here are some examples:

3x + 4x = 7x

2x2 + 7x2= 9x2

3xy + 6xy = 9xy

5x3 – 3x3 = 2x3

What do you do with exponents when you are adding? Nothing! That's right, you add only the coefficients. The variables and their exponents stay the same. This is not a new concept. You used it in previous lessons when you combined similar terms.

Multiplying with Exponents

The rules for multiplying expressions with exponents may appear to be confusing. You treat exponents differently from ordinary numbers. You would think that when you are multiplying, you would multiply the exponents. However, that's not true. When you are multiplying expressions, you add the exponents. Here's an example of how to simplify an expression.

Example:

x2 · x3

(x · x)(x · x · x)

x5

You can see that you have 5 x's, which is written as x5. To get x5 for an answer, you add the exponents instead of multiplying them.

Tip

When an expression is written as x2x5, it implies multiplication. You do not need to use the multiplication symbol.

 

Example:

a3 · a4

(a · a · a)(a · a · a · a)

a7

The factors of a3 are a · a · a. The factors of a4 are a · a · a · a. The factored form of a3 · a4 is a · a · a · a · a · a · a. When you write the problem out in factor form, you can see that you have 7 a's. The easy way to get 7 is to add the exponents.

What would you do if you see an expression like x20, and you want to multiply it by x25? You can see that writing out the factors of x20 · x25 would take a long time. Think about how easy it would be to make a mistake if you wrote out all the factors. It is much more efficient and fast to use the rule for multiplying exponents: When you are multiplying, you add the exponents.

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