math f.2

[3 - (r + s)2 + (r - s)2]2
= {3 + [(r - s)2 - (r + s)2]}2
Using the identity of a2 - b2 = (a + b)(a - b)
= {3 + [(r - s + r + s)(r - s - r - s)]2
= [3 + (2r)(- 2s)]2
「 = [3 + (- 4rs)]2
Using the identity of (a + b)2 = a2 + 2ab + b2
= (3)2 + 2(3)(-4rs) + (-4rs)2
= 9 - 24rs + 16r2s2 」

由 「」開始，你可以用第 2 個方法：
:
:
= [3 + (- 4rs)]2
= (3 - 4rs)2
Using the identity of (a - b)2 = a2 - 2ab + b2
= (3)2 - 2(3)(4rs) + (4rs)2
= 9 - 24rs + 16r2s2

[3-(r+s)^2+(r-s)^2]^2
=[3-(r^2+2rs+s^2)+(r^2-2rs+s^2)]^2
=[3-r^2-2rs-s^2+r^2-2rs+s^2]^2
=(3-4rs)^2
=3^2-2(3)(4rs)+(4rs)^2
=9-24rs+16(r^2)(s^2)