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: \(n, c, j\)).