Question 323184
To rationalize a denominator you need to remove the radical.  When your denominator has more than one term, you multiply the numerator and denominator by the conjugate (opposite) of the denominator.  Meaning if your denominator is {{{sqrt(x)+sqrt(y)}}} the conjugate would be {{{sqrt(x)-sqrt(y)}}} 
so...
{{{(sqrt(x)-sqrt(y))/(sqrt(x)+sqrt(y))*(sqrt(x)-sqrt(y))/(sqrt(x)-sqrt(y))}}}
multiply by FOIL both the numerator and denominator
{{{((sqrt(x))^2-sqrt(xy)-sqrt(xy)+(sqrt(y))^2)/((sqrt(x))^2-(sqrt(y))^2))}}}
simplify
{{{(x-2sqrt(xy)+x)/(x-y)}}}