Question

expand: (x+y^2)(x+c-y^2)

Answer 1

multiply all the letters on the left bracket by each letter in the right bracket

Answer 2

We have:
\[
(x+y^2)(x+c-y^2)=(x+y^2)(x-y^2+c)=x^2-y^4+c(x+y^2)=\\
x^2-y^4+cx+cy^2
\]And, we are done.