Simplifying Radicals Formula

The Formula

\sqrt{ab} = \sqrt{a} \cdot \sqrt{b}, \quad \sqrt{\frac{a}{b}} = \frac{\sqrt{a}}{\sqrt{b}}, \quad \sqrt{a^2 \cdot b} = a\sqrt{b} \;(a \geq 0)

When to use: Look inside the radical for perfect squares hiding as factors. \sqrt{72} contains 36 \times 2, and since \sqrt{36} = 6, you can pull the 6 out: \sqrt{72} = 6\sqrt{2}. Think of it as freeing numbers that are 'ready' to leave the radical.

Quick Example

\sqrt{72} = \sqrt{36 \cdot 2} = 6\sqrt{2}
\sqrt{50x^2} = 5x\sqrt{2}

Notation

\sqrt{\phantom{x}} is the radical sign. The expression under it is the radicand. \sqrt[n]{a} is the nth root. Simplest form has no perfect square factors under the radical.

What This Formula Means

Simplifying a radical expression by extracting perfect square factors from under the radical sign so that no perfect square (other than 1) remains under the radical.

Look inside the radical for perfect squares hiding as factors. \sqrt{72} contains 36 \times 2, and since \sqrt{36} = 6, you can pull the 6 out: \sqrt{72} = 6\sqrt{2}. Think of it as freeing numbers that are 'ready' to leave the radical.

Formal View

\sqrt{a} = a^{1/2} for a \geq 0. The product rule \sqrt{ab} = \sqrt{a}\sqrt{b} (a, b \geq 0) follows from (ab)^{1/2} = a^{1/2} b^{1/2}. Simplest form: \sqrt{a^2 b} = |a|\sqrt{b} where b has no perfect square factors.

Worked Examples

Example 1

easy
Simplify \sqrt{72}.

Solution

  1. 1
    Step 1: Find the largest perfect square factor: 72 = 36 \times 2.
  2. 2
    Step 2: \sqrt{72} = \sqrt{36 \times 2} = \sqrt{36} \cdot \sqrt{2} = 6\sqrt{2}.
  3. 3
    Check: 6^2 \times 2 = 72 ✓

Answer

6\sqrt{2}
To simplify a radical, factor the radicand into a perfect square times a remaining factor. Extract the square root of the perfect square part. The goal is to have no perfect square factors under the radical.

Example 2

medium
Simplify \sqrt{50x^4y^3}.

Example 3

medium
Simplify \sqrt{200x^4y^3}.

Common Mistakes

  • Not extracting the largest perfect square factor: writing \sqrt{72} = 2\sqrt{18} instead of 6\sqrt{2}
  • Forgetting that \sqrt{x^2} = |x|, not just x (absolute value matters for even roots)
  • Incorrectly splitting addition under the radical: \sqrt{a + b} \neq \sqrt{a} + \sqrt{b}

Why This Formula Matters

Simplest radical form is the standard way to express answers. It is required for adding and subtracting radicals (like terms must have the same radicand).

Frequently Asked Questions

What is the Simplifying Radicals formula?

Simplifying a radical expression by extracting perfect square factors from under the radical sign so that no perfect square (other than 1) remains under the radical.

How do you use the Simplifying Radicals formula?

Look inside the radical for perfect squares hiding as factors. \sqrt{72} contains 36 \times 2, and since \sqrt{36} = 6, you can pull the 6 out: \sqrt{72} = 6\sqrt{2}. Think of it as freeing numbers that are 'ready' to leave the radical.

What do the symbols mean in the Simplifying Radicals formula?

\sqrt{\phantom{x}} is the radical sign. The expression under it is the radicand. \sqrt[n]{a} is the nth root. Simplest form has no perfect square factors under the radical.

Why is the Simplifying Radicals formula important in Math?

Simplest radical form is the standard way to express answers. It is required for adding and subtracting radicals (like terms must have the same radicand).

What do students get wrong about Simplifying Radicals?

Finding the largest perfect square factor. It helps to factor the radicand completely into primes first.

What should I learn before the Simplifying Radicals formula?

Before studying the Simplifying Radicals formula, you should understand: square roots, factors.

← Back to Simplifying Radicals See All Examples Practice Problems