\[= - 35b^{2} + 72b - 4 > 0\]
\[- 35b^{2} + 72b - 4 = 0\]
\[D = 5184 - 560 = 4624\]
\[b_{1} = \frac{- 72 + 68}{- 70} = \frac{2}{35}\]
\[b_{2} = \frac{- 72 - 68}{- 70} = 2\]
\[\frac{2}{35} < b < 2.\]
\[Уравнение\ становится\ \]
\[линейным\ и\ имеет\ один\ \]
\[корень\ при:\]
\[3b - 2 = 0\]
\[3b = 2\]
\[b = \frac{2}{3}.\]
\[Ответ:\left( \frac{2}{35};\frac{2}{3} \right) \cup \left( \frac{2}{3};2 \right).\]