\(f\left(a\right)=\sqrt{25a^2-30a+9}=\sqrt{\left(5a-3\right)^2}=\left|5a-3\right|\)
\(g\left(a\right)=a\)
\(\Rightarrow\left|5a-3\right|=a+7\)
Nếu \(a\ge\frac{3}{5}\Rightarrow\left|5a-3\right|=5a-3\)
\(\Rightarrow5a-3=a+7\Leftrightarrow a=\frac{5}{2}\left(tm\right)\)
Nếu \(a< \frac{3}{5}\Rightarrow\left|5a-3\right|=3-5a\)
\(\Rightarrow3-5a=a+7\Leftrightarrow a=\frac{-2}{3}\left(tm\right)\)