Rational Exponents

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  • 0:06 Quick Review
  • 0:30 Rational to Radical
  • 1:20 Examples
  • 3:03 Lesson Summary
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Lesson Transcript
Instructor: Kathryn Maloney

Kathryn teaches college math. She holds a master's degree in Learning and Technology.

In this video, learn how to go from a rational exponent to a radical expression and back. No tricks or magic, just good math! We'll review the basics and look at a few examples.

Quick Review

Now, remember, a rational number is any number that can be written as a fraction. If that's true, what is a rational exponent? A rational exponent is an exponent that is written as a fraction. Here are a couple examples: x^(2/3), y^(1/2).

A rational exponent is an exponent that is written as a fraction
Rational Exponent

You'll notice that the exponent is a fraction. So what is the fraction telling us? The fraction refers to a radical. Let's look at a radical expression.

Rational to Radical

First, we have the radical symbol. The b is called the index or root number. Inside the radical is the radicand. For our example, x^a is the radicand.

How does that convert to a fractional exponent? Here's what the radical and rational exponent look like together. As you can, see the b in the denominator is the same as the index for the radical. The a in the numerator is the same as the exponent in the radicand.

There are two ways to rewrite a rational exponent: x^(a/b) = bth root of (x^a) = (bth root of x)^a. These all mean the same!

A Few Examples

Let me show you how this works. So, we have y^2/3 is the same thing as saying the cube root (it's the cube root because we have a 3 here) of y^2. Well, that's the same thing as saying (cube root of y)^2.

Let's look at another one. Here we have the fifth root of x^3. The fifth root is rewritten as the denominator in the rational exponent fraction. The exponent 3 is written as the numerator in the rational exponent fraction. So, the fifth root of x^3 is rewritten as x^(3/5).

Here's the next example: the seventh root of the quantity (2x)^5. How would that look as a rational exponent? The quantity (2x)^(5/7). Remember, the denominator of the rational fraction is the radicand exponent and the numerator is the index number.

Without parentheses around the 4x, only the x is raised to the 1/2 power
example of rational exponent

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