Решите уравнение (7x+1)(x−3)+20(x−1)(x+1)=3(3x–2)^2+13.

\[(7x + 1)(x - 3) + 20(x - 1)(x + 1) = 3(3x - 2)^{2} + 13\]

\[7x^{2} + x - 21x - 3 + 20x^{2} - 20 = 3 \cdot \left( 9x^{2} - 12x + 4 \right) + 13\]

\[27x^{2} - 20x - 23 = 27x^{2} - 36x + 12 + 13\]

\[- 20x + 36x = 25 + 23\]

\[16x = 48\]

\[x = 3.\]

\[Ответ:x = 3.\]