Tìm x

3 tìm x
a, x^2-16=0
b, 9x^2-25=0
c, 4x^2-(2x+1)^2=0
d, (x+2)(x^2-2x+4)-x(x+3)(x-3)=26
e, (x-3)(x^2+3x+9)-x(x-4)(x+y)=21