Решение:
\((5x - 1)(x + 2) + 3(x - 4)(x + 4) = 2(2x + 3)^2 - 8\)
\(5x^2 + 10x - x - 2 + 3(x^2 - 16) = 2(4x^2 + 12x + 9) - 8\)
\(5x^2 + 9x - 2 + 3x^2 - 48 = 8x^2 + 24x + 18 - 8\)
\(8x^2 + 9x - 50 = 8x^2 + 24x + 10\)
\(9x - 50 = 24x + 10\)
\(-60 = 15x\)
\(x = -4\)
Ответ: \(x = -4\)