How do you rationalize the denominator of a fraction?

Questions which ask for you to rationalize the denominator usually includes an integer and a square root of a number (x+sqrt(y)).We can use the following formula to our advantage: (a+b)(a-b)=a^2-b^2. In this case, using x and y: (x+sqrt(y))(x-sqrt(y))=x^2-y, and we can see, that it eliminates the square root from the denominator.How can we achive this? By multiplying the fraction by 1, more specifically by (x-sqrt(y))/(x-sqrt(y)) or the other way around.