To rationationalise a denominator (this is to say making the bottom number of a fraction a rational interger) you must multily the whole fraction by what is on the bottom.

Eg. if there is 2 over 4root5 you must multiple both top and bottom by 4root5.

If there is more than one factor on the bottom of the eqution then you must multily it by the same factors but with the signs switched, in order to make this work.This will be the same as the difference of two squares.

Eg. if you have 2 over 4root5 + 7 you must muliply top and bottom by 4root5 - 7.

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