\(\begin{array}{l}f\left( 0 \right) = - 1\\ \Rightarrow b = - 1\\f\left( { - 2} \right) = 3 \Leftrightarrow - 2a - 1 = 3\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, \Leftrightarrow \, - 2a = 4\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, \Leftrightarrow \,\,\,\,\,\,\,\,a = - 2\\ \Rightarrow y = - 2x - 1\end{array}\)