вправа 449 гдз 7 клас алгебра Мерзляк Полонський

Відповідь:

1) (x - 3)(x + 7) - (x + 7)(x - 8) = 0;
(x + 7)(x - 3 - (x - 8)) = 0;
(x + 7)(x - 3 - x + 8) = 0;
(x + 7) · 5 = 0;
x + 7 = 0;
x = -7;
2) (4x - 9)(x - 2) + (1 - x)(x - 2) = 0;
(x - 2)(4x - 9 + 1 - x) = 0;
(x - 2)(3x - 8) = 0;
x - 2 = 0;
x = 2;
3x - 8 = 0; \begin{equation}x=2\frac{2}{3};\end{equation} 3) 0,2x(x - 5) + 8(x - 5) = 0;
(x - 5)(0,2x + 8) = 0;
x - 5 = 0;
x = 5;
0,2x + 8 = 0;
x = -40;
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;
x = 7;
14 - x = 0;
x = 14.