Expand the polynomial (x2 − y2)2 + (2xy)2, then simplify it by combining like terms.

To expand it, you basically take two of everything in the parentheses and add addition or subtraction signs. Once you're done it will look like this:
x^2-y^2+x^2-y^2+2xy+2xy
Then you combine the like terms. In this expression, the like terms are x^2, -y^2, and 2xy. The final expression will look like this: 2x^2-2y^2+4xy