9x^2=16(x+1)^2
16(x+1)^2 - 9x^2 = 0
[4(x+1)]^2 - (3x)^2 = 0
[4(x+1)+3x] * [4(x+1)-3x] = 0
(7x+4)(x+4) = 0
x=-4,或 x= -4/7