a) \(\dfrac{1}{x}< 2\Leftrightarrow\dfrac{1-2x}{x}< 0\Leftrightarrow\left[{}\begin{matrix}x>\dfrac{1}{2}\\x< 0\end{matrix}\right.\)
b) \(\dfrac{x^2+x-1}{1-x}>-x\Leftrightarrow\dfrac{x^2+x-1+x-x^2}{1-x}>0\)
\(\Leftrightarrow\dfrac{2x-1}{1-x}>0\Leftrightarrow\left\{{}\begin{matrix}x>\dfrac{1}{2}\\x< 1\end{matrix}\right.\)