Pure Surds and Mixed Surds: Definition Examples Conversion

In this section, we will learn about pure surds as well as mixed surds.

Table of Contents

Definition of Pure Surd

A surd is called a pure surd if it consists of a whole rational number under the root symbol.

For example, $\sqrt{2}$ is a pure surd but $7\sqrt{2}$ is not.

Examples of Pure Surd:

(i) $\sqrt{11}, \sqrt{18}$ are pure surds.

(ii) The surd $2^{3/2}$ is an example of pure surds. Note that $2^{3/2}$ $=\sqrt{2^3}$ $=\sqrt{8}.$

Definition of Mixed Surd

A surd is called a mixed surd if it is a product of a rational number and a surd. More precisely, a mixed surd is a product of a rational number and a pure surd.

For example, $7\sqrt{2}$ is a mixed surd.

Examples of Mixed Surd:

How to convert Pure Surds into Mixed surds

A pure surd may not always be transformed into a mixed surd. We will understand the fact with the help of examples.

Example 1: Convert the pure surd $\sqrt{8}$ into a mixed surd.

Note that $\sqrt{8}=\sqrt{2 \times 2 \times 2}$

$=\sqrt{2 \times 2} \times \sqrt{2}$

$=2\sqrt{2}$

So $2\sqrt{2}$ is the mixed surd-form of $\sqrt{8}.$

Example 2: Convert the pure surd $\sqrt[4]{8}$ into a mixed surd.

As $8$ cannot be expressed as a fourth-power of $2,$ it is not possible to simplify $\sqrt[4]{8}.$ So this surd is not a product of a rational and a surd. It’s a surd with only $8$ is under the root symbol. Thus, $\sqrt[4]{8}$ is a pure surd that cannot be converted into a mixed surd.

Summary: If some part of the rational number involved in a pure surd cannot be taken out after simplification, then that pure surd cannot be converted into a mixed surd. But we can always convert a mixed surd into a pure surd.

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FAQs on Pure and Mixed Surds

Q1: What are pure surds?

Answer: A surd in which a whole rational number is under the root symbol, is called a pure surd. For example, √7 is a pure surd.

Q2: Give examples of pure surds.

Answer: √2, √5, √11 are examples of pure surds.

Q3: Is root 3 a pure surd?

Answer: As root 3 consists of a rational number 3 inside the root symbol, √3 is a pure surd.

Q4: What are mixed surds?

Answer: A surd which is a product of a rational number and an irrational number, is called a mixed surd. For example, 2√3, 4√2 are examples of mixed surds.

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