\[{\ (x - 3)}^{2} - (x + 1)^{2} = 12\]
\[x^{2} - 6x + 9 - x^{2} - 2x - 1 = 12\]
\[- 8x = 4\]
\[x = - 0,5\]
\[Ответ:\ x = - 0,5.\]