Rút gọn: a) (3x - 1)^2 - (x + 7)^2 - 2(5 - 2x)(2x + 5). b) (x + y)^3 - (x - y)^3 - 6x^2y

Rút gọn
a)(3x-1)^2-(x+7)^2-2(5-2x)(2x+5).
b)(x+y)^3-(x-y)^3-6x^2 y.
c)3(x^2+y^2+z^2)-(x-y)^2-(y-z)^2-(z-x)^2-2xy-2yz-2xz.