How to Solve Rational Exponents and Radicals?

By identifying powers and roots and converting them to radicals, we can write rational power exponents expressions as radicals. In this post, you learn more about rational exponents and radicals.

How to Solve Rational Exponents and Radicals?
Tutor-style math help

Solve Rational Exponents and Radicals: what to notice and how to work it

Radicals skill
Radicals are roots. Simplifying or solving with radicals is mostly about perfect powers, domain restrictions, and checking for extraneous answers.

What to notice first

Look for perfect-square, perfect-cube, or matching index factors before reaching for a calculator.

Common student mistake

Do not split a radical across addition. \(\sqrt{a+b}\) is not usually \(\sqrt a+\sqrt b\).

Key formulas and cues

\(\sqrt{ab}=\sqrt a\sqrt b\)
\(x^{m/n}=\sqrt[n]{x^m}\)
\(\sqrt{x}\text{ requires }x\ge0\)
\(\text{squaring can create extraneous answers}\)
domain starts

A reliable path

  1. Find perfect powersBreak the radicand into a perfect power times a leftover factor.
  2. Watch the domainEven roots need nonnegative radicands in real-number problems.
  3. Check solutionsIf you squared both sides, test answers in the original equation.

Worked examples

Simplify a radical

Example: \(\sqrt{72}\)
  1. 72 = 36 times 2.
  2. The square root of 36 is 6.
  3. Leave the leftover 2 inside.
Answer: \(6\sqrt2\)

Find a radical domain

Example: \(y=\sqrt{x-4}\)
  1. The radicand is x – 4.
  2. Require x – 4 >= 0.
  3. Solve the inequality.
Answer: \(x\ge4\)
Try one before moving on
Try: Simplify \(\sqrt{98}\).
Answer: \(7\sqrt2\).
Next step: do the matching worksheet or quiz while the method is still fresh, then come back and explain the first step in your own words.

An expression with a rational exponent is equivalent to a radical in which the denominator is the index and the numerator is the exponent. Any radical expression can be written with a rational exponent, which we call exponential form.

Related Topics

A step-by-step guide to rational exponents and radicals

By identifying powers and roots and converting them to radicals, we can write rational power exponents expressions as radicals. Consider the rational exponents’ expression \(a^{\frac{m}{n}}\). Now, follow the steps given:

  1. Identify power by looking at the numerator of the rational exponent. Here in the rational exponent \(a^{\frac{m}{n}}\), \(m\) is the power.
  2. Identify the root by looking at the denominator of the rational exponent. Here in rational exponent \(a^{\frac{m}{n}}\), \(n\) is the root.
  3. Write the base as the radicand, power raising to the radicand, and the root as the index. Here we can write \(a^{\frac{m}{n}}=\sqrt[n]{a^m}\).

We can also convert radicals into rational exponents. Consider the square root of the positive number \(\sqrt{a}\). We can write the square of \(\sqrt{a}\) as a rational exponent. \(\sqrt{a}=a^{\frac{1}{2}}\) which is a rational exponent.

Rational Exponents and Radicals – Example 1:

Express \((2x)^{\frac{1}{3}}\) in radical form.

Solution:

\((2x)^{\frac{1}{3}}\) \(=\)\(\sqrt[3]{2x}\)

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Rational Exponents and Radicals – Example 2:

Write \(\sqrt[4]{81}\) as an expression with a rational exponent.

Solution:

\(\sqrt[4]{81}=81^{\frac{1}{4}}\)

Exercises for Rational Exponents and Radicals

Rewrite the expression in radical form or rational exponent.

  1. \(\color{blue}{6\sqrt[3]{xy}}\)
  2. \(\color{blue}{27^{\frac{2}{3}}}\)
  3. \(\color{blue}{\sqrt[2]{\left(5ab\right)^3}}\)
  4. \(\color{blue}{\left(10\:r\right)^{-\frac{3}{4}}}\)
  5. \(\color{blue}{\frac{1}{\sqrt[5]{\left(6x\right)^3}}}\)
Answers
  1. \(\color{blue}{6\left(xy\right)^{\frac{1}{3}}}\)
  2. \(\color{blue}{\sqrt[3]{27^2}}\)
  3. \(\color{blue}{\left(5ab\right)^{\frac{3}{2}}}\)
  4. \(\color{blue}{\frac{1}{\sqrt[4]{\left(10\:r\right)^3}}}\)
  5. \(\color{blue}{\left(6x\right)^{-\frac{3}{5}}}\)

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