Question

因式分解(1-X^2)(1-Y^2)-4XY

Answer 1

(1-X^2)(1-Y^2)-4XY

=1 - X^2 - Y^2 + X^2 * Y^2 - 4XY

=( 1 - 2XY + X^2 * Y^2 ) - ( X^2 + 2XY + Y^2 )

=( 1 - XY )^2 - ( X + Y )^2

=( 1 - XY + X + Y )( 1 - XY - X - Y )