4) 7(x - 7) -(x - 7)² = 0; (x - 7)(7 - (x - 7)) = 0; (x - 7)(7 - x + 7) = 0; (x - 7)(14 - x) = 0; x - 7 = 0 или 14 - x = 0; x = 7 или x = 14.
Ответ: x = 7, x = 14