Lời giải:
2.
Ta có:
$15 \vdots (7-x)$
$=>(7-x)∈U(15)=${$-15;-5;-3;-1;1;3;5;15$}
$7-x=-15<=>x=22$
$7-x=-5<=>x=12$
$7-x=-3<=>x=10$
$7-x=-1<=>x=8$
$7-x=1<=>x=6$
$7-x=3<=>x=4$
$7-x=5<=>x=2$
$7-x=15<=>x=-8$
Vậy $x=${$-8;2;4;6;8;10;12;22$} thì $15$ là bội của $7-x$
4.
d)
$\frac{x}{32}=\frac{2}{x}$
$<=>x.x=32.2$
$<=>x^2=64$
$<=>x=\sqrt{64}$
$<=>x=±8$
