\(P=2a^{n+1}+5a^{n+1}+3a^{n+1}-3a^n-7a^n\)
\(P=\left(2+5+3\right)a^{n+1}-\left(3+7\right)a^n\)
\(P=10.a^{n+1}-10.a^n\)
b/ \(P=0\Rightarrow10.a^{n+1}-10.a^n=0\)
\(\Rightarrow a^{n+1}-a^n=0\)
\(\Rightarrow a^n\left(a-1\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}a^n=0\\a-1=0\end{matrix}\right.\) \(\Rightarrow\left[{}\begin{matrix}a=0\\a=1\end{matrix}\right.\)