maths question:Expand (x+1)^2(x-1)^2

(x+1)^2(x-1)^2

=[(x+1)(x-1)]^2

=[x^2-1]^2

=x^4-2x^2+1 [from (x-1)^2, but the unknown x is squared]

(x 1)^2(x-1)^2
=(x 1)(x 1)(x-1)(x-1)
=(x^2 2x 1)(x^2-2x 1)
=x^4 2x^3 x^2-2x^3-4x^2-2x x^2 2x 1
=x^4-2x^2 1

2008-07-21 22:17:18 補充：
對不起，出不到plus sign。

(x十1)^2(x-1)^2
=(x十1)(x十1)(x-1)(x-1)
=(x^2十2x十1)(x^2-2x十1)
=x^4十2x^3十x^2-2x^3-4x^2-2x十x^2十2x 1
=x^4-2x^2十1