logarithm question

[log(3x + 4)]/logx = 2
log(3x + 4) = 2 log x
log(3x + 4) = log (x^2)
3x + 4 = x^2
x^2 - 3x - 4 = 0
(x - 4)(x + 1) = 0
x = 4 or x = -1 (rejected because x > 0)