1.3.15

Rationalise Denominator

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Rationalising the Denominator

It is often easier to work with surds when there are no square roots on the bottom of a fraction. Removing surds from the bottom of a fraction is called ‘rationalising the denominator’.

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Advanced example

  • To rationalise a denominator of the form a ± √b multiply by the denominator but with the sign in front of the root changed.
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Exact form

  • Leaving an answer in exact form means leaving any fractions, surds and constants like in the expression rather than giving the answer as a decimal.

Jump to other topics

1Number

1.1Using Numbers

1.2Fractions, Decimals & Percentages

1.3Powers & Roots

1.4Accuracy

2Algebra

2.1Introduction to Algebra

2.2Manipulating Algebra

2.3Proofs & Functions

2.4Straight Line Graphs

2.5Common Graphs

2.6Transformations & Tangents

2.7Properties of Graphs

2.8Solving Equations

2.9Inequalities

2.10Sequences

3Ratio

4Geometry

4.1Introduction to Geometry

4.2Triangles & Quadrilaterals

4.3Transformations

4.4Circle Basics

4.5Circle Theorems

4.6Measurements & Units

4.7Calculating Area

4.8Triangle Formulae

4.93D Shapes

4.10Vectors

5Probability

6Statistics

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