The Power Rule for Exponents

Learning Objectives

  • Use the power rule to simplify expressions involving products, quotients, and exponents

 

Raise powers to powers

Another word for exponent is power.  You have likely seen or heard an example such as 35 can be described as 3 raised to the 5th power. In this section we will further expand our capabilities with exponents. We will learn what to do when a term with a power is raised to another power, and what to do when two numbers or variables are multiplied and both are raised to an exponent.  We will also learn what to do when numbers or variables that are divided are raised to a power.  We will begin by raising powers to powers.

Let’s simplify (52)4. In this case, the base is 52 and the exponent is 4, so you multiply 52 four times: (52)4=52525252=58 (using the Product Rule—add the exponents).

(52)4 is a power of a power. It is the fourth power of 5 to the second power. And we saw above that the answer is 58. Notice that the new exponent is the same as the product of the original exponents: 24=8.

So, (52)4=524=58 (which equals 390,625, if you do the multiplication).

Likewise, (x4)3=x43=x12

This leads to another rule for exponents—the Power Rule for Exponents. To simplify a power of a power, you multiply the exponents, keeping the base the same. For example, (23)5=215.

The Power Rule for Exponents

For any positive number x and integers a and b: (xa)b=xab.

Take a moment to contrast how this is different from the product rule for exponents found on the previous page.

Example

Simplify 6(c4)2.

Raise a product to a power

Simplify this expression.

(2a)4=(2a)(2a)(2a)(2a)=(2222)(aaaaa)=(24)(a4)=16a4

Notice that the exponent is applied to each factor of 2a. So, we can eliminate the middle steps.

(2a)4=(24)(a4), applying the 4 to each factor, 2 and a=16a4

The product of two or more numbers raised to a power is equal to the product of each number raised to the same power.

A Product Raised to a Power

For any nonzero numbers a and b and any integer x, (ab)x=axbx.

How is this rule different from the power raised to a power rule? How is it different from the product rule for exponents on the previous page?

Example

Simplify. (2yz)6

If the variable has an exponent with it, use the Power Rule: multiply the exponents.

Example

Simplify. (7a4b)2

Raise a quotient to a power

Now let’s look at what happens if you raise a quotient to a power. Remember that quotient means divide. Suppose you have 34 and raise it to the 3rd power.

(34)3=(34)(34)(34)=333444=3343

You can see that raising the quotient to the power of 3 can also be written as the numerator (3) to the power of 3, and the denominator (4) to the power of 3.

Similarly, if you are using variables, the quotient raised to a power is equal to the numerator raised to the power over the denominator raised to power.

(ab)4=(ab)(ab)(ab)(ab)=aaaabbbb=a4b4

When a quotient is raised to a power, you can apply the power to the numerator and denominator individually, as shown below.

(ab)4=a4b4

A Quotient Raised to a Power

For any number a, any non-zero number b, and any integer x, (ab)x=axbx.

Example

Simplify. (2x2yx)3

In the following video you will be shown examples of simplifying quotients that are raised to a power.

Summary

  • Evaluating expressions containing exponents is the same as evaluating any expression. You substitute the value of the variable into the expression and simplify.
  • The product rule for exponents: For any number x and any integers a and b(xa)(xb)=xa+b.
  • The quotient rule for exponents: For any non-zero number x and any integers a and b: xaxb=xab
  • The power rule for exponents:
    1. For any nonzero numbers a and b and any integer x, (ab)x=axbx.
    2. For any number a, any non-zero number b, and any integer x, (ab)x=axbx