Rationalisation (mathematics)

For the fundamental technique, the numerator and denominator must be multiplied by the same factor.

The cube root disappears from the denominator, because it is cubed; so

and applying the difference of two squares identity, which here will yield −1. To get this result, the entire fraction should be multiplied by

This technique works much more generally. It can easily be adapted to remove one square root at a time, i.e. to rationalise