When doing questions like this you simply times the top and bottom of the fraction by the bottom function but with a sign change. For example if "5 - **√**3" was the denominator of the fraction (on the bottom of the fraction) you would times the top and bottom of the fraction by "5 + **√**3". Note that it is only the sign in front of the surd that changes.

Here is a worked example of an exam question:

(4 + 2**√**2) / (2 - **√**2)

(4 + 2**√**2)(2 + **√**2) / (2 - **√**2)(2 + **√**2)

Use FOIL to expand the brackets: (8 + 4**√**2 + 4**√**2 + 4) / (4 + 2**√**2 - 2**√**2 -2)

SIMPLIFY

(12 + 8**√**2) / 2 = 6 + 4**√**2