Tính: a) (x-1)^3-x(x-2)^2+x-1; b) (x+1)^2-(x-1)^2-3(x-3)(x+3)

a) (x-1)^3-x(x-2)^2+x-1
b) (x+1)^2-(x-1)^2-3(x-3)(x+3)
c) (x-1)^3-(x+1)^3+6(x+1)(x-1)
d) (x+y)^3-(x-y)^3-2y^3
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