Answer :
x^2 - y^2 = 8
x^2 + y^2 = 4
Therefore: (x^2 - y^2 ) * (x^2 + y^2 ) = 8 *4
Expanded: x^4 + x^2 y^2 - x^2 y^2 - y^4 = 32
So: x^4 - y^4 = 32
x^2 + y^2 = 4
Therefore: (x^2 - y^2 ) * (x^2 + y^2 ) = 8 *4
Expanded: x^4 + x^2 y^2 - x^2 y^2 - y^4 = 32
So: x^4 - y^4 = 32