Tìm x

a) (x+1)^3 - (x-1)^3 -6(x-1)(x+1) b) x(x-1)(x+1)-(x+1)(x^3-x+1) c) (x-1)^3 -(x+2)(x^2-2x+4)+3(x+4)(x-4) d) 3x^2(x+1)(x-1)+(x^2-)^3-(x^2-1)(x^4+x^2+1)