`(x - 3)^2 - (3x + 4)^2 = 0`

`(x - 3)^2 = (3x + 4)^2`

\(\left[ \begin{array}{l}x - 3 = 3x + 4\\3 - x = 3x + 4\end{array} \right.\)

\(\left[ \begin{array}{l}-1 = 4x\\-7 = 2x\end{array} \right.\) 

Vậy `x = -1/4` hoặc `x = -7/2` 

`_________`

`***Rich`