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


1.1Place Value

1.2Factors & Multiples


1.4Fractions, Decimals & Percentages

1.5Growth & Decay

1.6Measurements & Units



3Ratio, Proportion & Rates of Change

4Geometry & Measures



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