Chứnh minh: a. $(a^2-b^2)(c^2-d^2) = (ac + bd)^2 - (ab + cd)^, b. 2(a^3 + b^3 +c^3 - abc) = (a + b + c)^2\left[(a-b)^2 + (b-c)^2 + (c-a)^2\right]$

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1) CMR
a.

$(a^2-b^2)(c^2-d^2) - (ac + bd)^2 - (ab + cd)^2$
b.

$h^2(a^3 + b^3 - abc) = (a + b + c)^2\left[(a-b)^2 + (b-c)^2 + (c-a)^2\right]$
c.

$(a+b)(b+c)(c+a) = (a+b)^2(c+a)^2 + a(b+c)^2 + b(c+a)^2$
d.

$(a+b+c)^3 = a^3 + b^3 + c^3 + 3(a+b)(b+c)(c+a)$

2) Cho

$x^2 + y^2 = -ny + 2y + 2x$ (MR:

$n, c, j$ ).

Chứnh minh: a. (a2−b2)(c2−d2)=(ac+bd)2−(ab+cd),b.2(a3+b3+c3−abc)=(a+b+c)2[(a−b)2+(b−c)2+(c−a)2](a^2-b^2)(c^2-d^2) = (ac + bd)^2 - (ab + cd)^, b. 2(a^3 + b^3 +c^3 - abc) = (a + b + c)^2\left[(a-b)^2 + (b-c)^2 + (c-a)^2\right]