Question 209827
x(sqrt{8y}) + 3(sqrt{2x^2}y})

Leave y inside for both square roots.

x(sqrt{8y}) becomes 2x(sqrt{2y}).

3(sqrt{2x^2}y})becomes 3x(sqrt{2y}).

We now have the same radicand 2y.  See it?

We can now add these two guys.

2x(sqrt{2y})+ 3x(sqrt{2y}) = 5x(sqrt{2y})

NOTE: You can only add or subtract radicals that have the same radicands.