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A4. Real numbers : rationalise a denominator. In any fraction, such as ¾ for example, the number on top, 3, is called the numerator and the number on the bottom, 4, is called the denominator. If a fraction has as its denominator a surd, then we can use the fact that n x n=n, to make the denominator into an integer. This process is called rationalising the denominator. An example The number 3/5 has a surd in its denominator. Using the rules for multiplying fractions and the fact that 5÷5=1, we get: The denominator is now an integer, 5. You should be able to make exact calculations, without a calculator, using and simplifying surds as appropriate. Simplify this surd by rationalising the denominator. Then check to see if you are correct. Press the button to get started.      =