\[bx² + (7b2)x + b = 0\]
\[D = 49b^{2} + 28b + 4 - 4b^{2} =\]
\[= 45b^{2} + 28b + 4 > 0\]
\[45b² + 28b + 4 = 0\]
\[D = 784 - 720 = 64\]
\[b_{1} = \frac{- 28 + 8}{90} = - \frac{2}{9}\]
\[b_{2} = \frac{- 28 - 8}{90} = - \frac{2}{5} = - 0,4\]
\[(b + 0,4)\left( b + \frac{2}{9} \right) > 0\]
\[b < - 0,4;\ \ b > - \frac{2}{9}.\]
\[При\ b = 0\ уравнение\ \]
\[становится\ линейным.\]