1.17.15

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’.

Advanced example

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.
Exact form

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.
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1

Number

1.1

Place Value & Ordering

1.2

Numerical Operations

1.3

Structure of Calculations

1.4

Fractions

1.5

Numerical Operations on Fractions

1.6

Roots & Powers

1.7

Numerical Skills

1.8

Factors & Multiples

1.9

Surds

1.10

Standard Form

1.11

Fractions, Decimals & Percentages

1.12

Percentage Change

1.13

Rounding & Estimation

1.14

Bounds & Accuracy

1.15

Using Numbers

1.16

Fractions, Decimals & Percentages

1.17

Powers & Roots

1.18

Accuracy

2

Algebra

2.1

Algebraic Notation

2.2

Substitution & Simplification

2.3

Brackets

2.4

Algebraic Fractions

2.5

Rearranging

2.6

Functions

2.7

Solving Linear Equations

2.8

Inequalities

2.9

Solving Quadratic Equations

2.10

Simultaneous Equations

2.11

Iteration

2.12

Sequences

2.13

Linear Graphs

2.14

Introduction to Algebra

2.15

Manipulating Algebra

2.16

Proofs & Functions

2.17

Straight Line Graphs

2.18

Common Graphs

2.19

Transformations & Tangents

2.20

Properties of Graphs

2.21

Solving Equations

2.22

Inequalities

2.23

Sequences

3

Ratio

3.1

Unit Conversions

3.2

Compound Units

3.3

Ratio Fundamentals

3.4

Advanced Ratio and Scale

3.5

Proportion

3.6

Algebraic Proportion

3.7

Ratios in Practice

3.8

Manipulating Ratios

3.9

Percentage & Interest

3.10

Proportion

3.11

Gradient

4

Geometry

4.1

Area & Perimeter

4.2

Angles

4.3

Trigonometry

4.4

Similarity & Congruence

4.5

Circle Geometry

4.6

Circle Theorems

4.7

Pythagoras

4.8

Surface Area

4.9

Volume

4.10

Vectors

4.11

Introduction to Geometry

4.12

Triangles & Quadrilaterals

4.13

Transformations

4.14

Circle Basics

4.15

Circle Theorems

4.16

Measurements & Units

4.17

Calculating Area

4.18

Triangle Formulae

4.19

3D Shapes

4.20

Vectors

5

Probability

6

Statistics

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