to simplify a radical, we break it up into perfect squares. For variables, even exponents are perfect squares.
448 = 64 * 7
x8 is a square
y19 = y18 * y
So, we have √64 * √7 * √x8 * √y18 * √y
= 8 * √7 * x4 * y9 * √y
Hope that helps!
BTW, on large numbers, you can also break them down a little at a time, if that helps.
For example, 448 = 4 * 4 * 4 * 7