[tex](3x-4)^2=(2x+1)^2\\
9x^2-24x+16=4x^2+4x+1\\
5x^2-28x+15=0\\
\Delta=784-4\cdot 5\cdot 15=484\Rightarrow \sqrt{\Delta}=22\\
x_1=\dfrac{28+22}{10}=\dfrac{50}{10}=5\\
x_2=\dfrac{28-22}{10}=\dfrac{6}{10}=\dfrac{3}{5}\\
\boxed{S:x\in \left \{5, \dfrac{3}{5}\right\}}[/tex]