tìm x
b) (x + 7) ^ 3 - (x - 7) ^ 3 - 6 * (x - 7) ^ 2 = - 70
c) (x - 1)(x ^ 2 + x + 1) + x(x + 2)(2 - x) = 5
d) (2x - 1) ^ 3 - 8x ^ 3 = (1 - 3x)(4x + 1)
e) (x + 2)(x ^ 2 - 2x + 4) - (x - 2)(x ^ 2 + 2x + 4) = 4x
f) (x + 3)(x ^ 2 - 3x + 9) - x(x ^ 2 + 7) = 5
