Giải thích các bước giải:
a.Ta có:
$8.2^n+2^{n+1}=8.2^n+2^n.2=2^n(8+2)=2^n.10\quad\vdots\quad 5$
b.Ta có:
$3^{n+3}-2.3^n+2^{n+5}-7.2^n$
$=3^{n}.3^3-2.3^n+2^{n}.2^5-7.2^n$
$=3^{n}.27-2.3^n+2^{n}.32-7.2^n$
$=3^{n}.(27-2)+2^{n}.(32-7)$
$=3^{n}.25+2^{n}.25$
$=25(3^n+2^n)\quad\vdots\quad 25$