Đáp án:
$\begin{array}{l}
a)\left( {b + 5} \right)\left( {b - 2} \right) > 0\\
\Rightarrow \left[ \begin{array}{l}
b > 2\\
b < - 5
\end{array} \right.\\
b)\left( {{b^2} - 1} \right)\left( {{b^2} - 10} \right) < 0\\
\Rightarrow 1 < {b^2} < 10\\
\Rightarrow \left[ \begin{array}{l}
- 3,16 < b < - 1\\
1 < b < 3,16
\end{array} \right.\\
c)\left( {{b^2} + 1} \right)\left( {{b^2} - 5} \right) < 0\\
\Rightarrow {b^2} < 5\\
\Rightarrow - 2,23 < b < 2,23
\end{array}$