Every binomial surd (a√ b + c√ d) has a conjugate counterpart (a√ b − c√ d). A property of the conjugate surd is that when you multiply a surd with its conjugate, the product will be a rational number (See Table below).
This is useful for rationalising fractions with surds in the denominators.
Example
Test Yourself!
Use the applet below to check your understanding of rationalising a denominator using the conjugate surd.