Giải thích các bước giải:
$3^{n+3}+3^{n+1}+2^{n+3}+2^{n+2}$
$= 3^{n+1}\left (3^{2}+1 \right )+2^{n+2}\left ( 2+1 \right )$
$= 3^{n+1}.10+3.2^{n+2}$
$= 3^{n+1}.2.5+3.2^{n+2}$
$= 3.2\left ( 3^{n}.5+2^{n+1} \right )$
$= 6\left ( 5.3^{n}+2^{n+1} \right )\vdots 6$