Question

Решите систему уравнений!

21x^2 + 39x - 6 < 0
x< 0

Answer 1

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