Put parentheses around it like this:




Form the conjugate of whichever you want to rationalize.
In this case the numerator.  The numerator is ,
It's conjugate is gotten by changing the sign of the second term.
So its conjugate is .

Now you put that over itself, like this and put it in 
parentheses:



Now you multiply these together:



Now you FOIL out the tops and the bottoms:



The middle two terms on top cancel:



And the two terms add together on the bottom:



Now we know the square roots of 25 and 4 so we get







Factor 2 out of the bottom:



Cancel the 2's:





Now the numerator is rational, because it doesn't
contain any square roots.

Edwin