Решите систему уравнений! 21x^2 + 39x - 6 < 0 x< 0

Решите задачу:

$21 x^{2} +39x-6\ \textless \ 0 \\ x\ \textless \ 0 \\ \\ 21 x^{2} +39x-6=0|:3 \\ 7 x^{2} +13x-2=0 \\ D=169+56=225 \\ \sqrt{D} =15 \\ x_{1} = \frac{-13+15}{14} = \frac{2}{14} = \frac{1}{7} \\ x_{2} = \frac{-13-15}{14} = \frac{-28}{14} =-2 \\ \\ x\in (-2; \frac{1}{7} ) \\ x\ \textless \ 0 \\ x\in (-2;0)$