a) Để hàm số đồng biến \(\Leftrightarrow5-3a>0\) \(\Leftrightarrow a< \dfrac{5}{3}\)
b) Ta có: \(f\left(-2\right)=10\) \(\Rightarrow\left(5-3a\right)\cdot\left(-2\right)+2=10\) \(\Rightarrow a=3\)
\(\Rightarrow f\left(2\right)=\left(5-3\cdot3\right)\cdot2+2=-6\)