Question

分解因式：（x²+y²-1）²-4x²y²

Answer 1

：（x²+y²-1）²-4x²y²

=（x²+y²-1+2xy)(x²+y²-1-2xy)

=[(x+y)²-1][(x-y)²-1]

=(x+y+1)(x+y-1)(x-y+1)(x-y-1)