1.
a) $35\vdots{x}$ => x∈Ư(35) mà x<10 => $x∈{1,5,7}$
b) $231\vdotsx$ => x∈Ư(231) mà 15<x<230 => $x∈{13}$
c) $18\vdots(x+2)$ =>$16\vdotx$ => x∈Ư(16) => $x∈{±1,±2,±4,±8,±16}$
d) $x∈B(14)$ => x∈{28,42,...} mà 28≤x≤70 => $x∈{28,42,56,70}$
e) $x\vdots13$ => x∈B(13) mà 20<x≤70 => $x∈{26,39,52,65}$