№ 6 Решите уравнение: (7x + 1)(x-3)+20(x - 1)(x + 1) = 3(3x - 2)² + 13.

\[(7x + 1)(x - 3) + 20(x - 1)(x + 1) = 3(3x - 2)^2 + 13\] \[7x^2 - 21x + x - 3 + 20(x^2 - 1) = 3(9x^2 - 12x + 4) + 13\] \[7x^2 - 20x - 3 + 20x^2 - 20 = 27x^2 - 36x + 12 + 13\] \[27x^2 - 20x - 23 = 27x^2 - 36x + 25\] \[-20x + 36x = 25 + 23\] \[16x = 48\] \[x = 3\]

Ответ: x = 3