(7x-1)(x-1)=16 Пожалуйста

$(7x - 1)(x - 1) = 16 \\ 7x {}^{2} - 7x - x + 1 = 16 \\ 7x {}^{2} - 8x + 1 - 16 = 0 \\ 7x {}^{2} - 8x - 15 = 0 \\ d = b {}^{2} - 4ac =( - 8) {}^{2} - 4 \times 7 \times ( - 15) = 64 + 420 = 484 \: \: \: (22) \\ x = \frac{ - b + - \sqrt{d} }{2a} = \frac{8 + - 22}{2 \times 7} = \frac{ - 14}{14} \: \: or \: \: \frac{30}{14} = - 1 \: \: or \: \: \frac{15}{7} = - 1 \: \: or \: \: 2 \frac{1}{7}$

Ответ : -1; 2 1/7