You use a conjugate to rationalize a denominator with a square root in it.
For example, take [tex]\frac{1}{5-\sqrt{3}}[/tex]
To rationalize, you need to multiply by [tex]\frac{5+\sqrt{3} }{5+\sqrt{3}}[/tex]
That would get you [tex]\frac{5+\sqrt{3}}{22}[/tex]
