Question

Solve $9^{x+2}=720+9^x$

Answer 1

$9^{x+2}=720+9^x\Rightarrow 9^x\times 9^2-9^x=720\Rightarrow 9^x(9^2-1)=720\Rightarrow 9^x\times 80=720$

$\Rightarrow 9^x=\frac{720}{80}\Rightarrow 9^x=9^1$

$\therefore x=1$