Question

which expression is equivalent to x^4-y^4?

Answer 1

$x^4-y^4=(x^2)^2-(y^2)^2=(x^2-y^2)(x^2+y^2)\\\\=(x-y)(x+y)(x^2+y^2)\\\\\\\\a^2-b^2=(a-b)(a+b)$

Answer 2

$x^4-y^4=(x^2)^2-(y^2)^2=(x^2-y^2)(x^2+y^2)=(x-y)(x+y)(x^2+y^2)$