Tìm x: a) x^3 - 9x = 0; b) x^2 + 64 = 16x; c) 2x(2x - 3) - (2x + 1)^2 = 9

Tìm x:
a. x^3 - 9x = 0
b. x^2 + 64 = 16x
c. 2x (2x - 3) - (2x + 1)^2 = 9