[tex]x^2-4x=12\\\\x^2-2x\cdot2=12\ \ \ |add\ 2^2\ to\ both\ sides\\\\x^2-2x\cdot2+2^2=12+2^2\ \ \ \ \ |use\ a^2-2ab+b^2=(a-b)^2\\\\(x-2)^2=12+4\\\\(x-2)^2=16\iff x-2=\pm\sqrt{16}\\\\x-2=-4\ or\ x-2=4\ \ \ |add\ 2\ to\ both\ sides\\\\\boxed{x=-2\ or\ x=6}[/tex]
