Taking Factors Out of a Root

To extract factors from a root, we group the repeated factors of the radicand as indicated by the index: in a square root (index $2$), each group of $2$ equal factors comes out as a single factor; in a cube root (index $3$), each group of $3$ comes out.

Look at the following diagram representing $\sqrt[3]{x^4}$. As $x^4 = x^3 \cdot x$, the group of $3$ comes out as a single $x$ and the remaining factor stays inside.

Following this logic, extract all possible factors from the following roots:

1. a) $\sqrt{x^3}$
2. b) $\sqrt{a^5}$
3. c) $\sqrt[3]{m^4}$
4. d) $\sqrt[4]{y^5}$

Many times we find numbers that are not factorised. The first step must always be to decompose the number into prime factors.

For example, to simplify $\sqrt{12}$, we first think that $12 = 2^2 \cdot 3$. As $2$ is squared, it can "escape" from the square root.

Decompose into prime factors and extract as much as you can from these square roots:

1. a) $\sqrt{18}$
2. b) $\sqrt{50}$
3. c) $\sqrt{20}$
4. d) $\sqrt{75}$

We have a square plot of land. We know that its area is $72 \text{ m}^2$, but we want to know exactly how long its side is, expressed in the simplest possible form (by extracting factors).

Remember that if the Area of a square is $l^2$, then the side is $l = \sqrt{\text{Area}}$.

1. Factorise the number 72.

2. Write $\sqrt{72}$ using those factors.

3. Extract the numbers that are squared.

Extract all possible factors from the following numerical radicals. To do this, you must first find the prime factor decomposition of the numbers inside the root.

1. a) $\sqrt{216}$
2. b) $\sqrt[3]{5000}$
3. c) $\sqrt[4]{162}$

Sometimes we have numbers and letters mixed inside a root. The procedure is the same: we work with the number on one side and with each letter on the other.

Simplify the following radicals by extracting all possible factors:

1. a) $\sqrt{8x^3}$
2. b) $\sqrt{27a^2}$
3. c) $\sqrt{16y^5}$
4. d) $\sqrt{25z^3}$

We can not only extract factors from the numerator, but also from the denominator if we have fractions inside the root.

If we have $\sqrt{\frac{a^3}{b^2}}$, we can take factors out from top and bottom independently. In this example, $b^2$ comes out as $b$ in the denominator, and from $a^3$ we take out an $a$ in the numerator: $\frac{a}{b}\sqrt{a}$.

Try to simplify these expressions:

1. a) $\sqrt{\frac{50}{9}}$
2. b) $\sqrt{\frac{x^3}{4}}$
3. c) $\sqrt{\frac{1}{27}}$ (Hint: factorise 27 and leave it in the denominator)

Simplify the following radicals containing variables. Remember that to be able to extract a variable, its exponent must be equal to or greater than the index of the root.

1. a) $\sqrt[3]{x^4 \cdot y^7 \cdot z^{10}}$
2. b) $\sqrt{25a^3 b^5 c}$
3. c) $\sqrt[5]{\frac{m^7}{n^{10}}}$

Let's play the inverse process to check if you have understood extraction. If I have a factor outside the root and I want to put it inside, I have to raise it to the index of the root.

For example: $3\sqrt{2} = \sqrt{3^2 \cdot 2} = \sqrt{9 \cdot 2} = \sqrt{18}$.

In your exercise book, match each simplified expression on the left with its original root on the right (you don't need to calculate, just reason which number came out):

1. $2\sqrt{2}$ --- A. $\sqrt{12}$

2. $3\sqrt{2}$ --- B. $\sqrt{20}$

3. $2\sqrt{3}$ --- C. $\sqrt{8}$

4. $2\sqrt{5}$ --- D. $\sqrt{18}$

State whether the following equalities are true or false by carrying out the necessary factor extraction:

1. a) $\sqrt{a^2 + b^2} = a + b$
2. b) $\sqrt{16 \cdot x^6} = 4x^3$
3. c) $\sqrt[3]{8 + 27} = 5$
4. d) $\sqrt{\frac{x^2}{4}} = \frac{x}{2}$

In order to add or subtract radicals, they must be like radicals. At first glance, the following radicals appear different. Extract factors from each of them to check whether their radical parts are the same and, if so, express them in simplified form:

1. a) $\sqrt{80}$
2. b) $\sqrt{125}$
3. c) $2\sqrt{45}$

Simplify the following fractions containing radicals by extracting factors from both the numerator and the denominator. If possible, simplify the resulting fraction:

1. a) $\sqrt{\frac{98}{75}}$
2. b) $\sqrt[3]{\frac{16a^4}{27b^3}}$