(2X^2+63y^2)(2x^2-63y^2)
Assuming x = X:
set: a = 2X^2 and b = 63y^2
(a + b)(a - b) = a^2 - b^2=
(2X^2)^2 - (63y^2)^2 =
4X^4 - 3969y^4
Assuming x =/= X:
(2X^2+63y^2)(2x^2-63y^2)
Set: a = 2X^2, b= 63y^2 and c = 2x^2
(a + b)(c - b) = ac - ab + bc - b^2 = a(c - b) + b(c - b) =
(2X^2)(2x^2 - 63y^2) + (63y^2)(2x^2 - 63y^2) =
4(X^2)(x^2) - 126(X^2)(y^2) + 126(x^2)(y^2) - 3969 y^4