Rationalising-Denominators Edexcel Higher

Rationalising denominators

What does rationalising the denominator mean?

• If a fraction has a denominator containing a surd then it has an irrational denominator

  • E.g. or

• The fraction can be rewritten as an equivalent fraction, but with a rational denominator

  • E.g. or

• The numerator may contain a surd, but the denominator is rationalised

How do I rationalise simple denominators?

• If the denominator is a surd:

  • Multiply the top and bottom of the fraction by the surd on the denominator

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