Đáp án:
1)$ x=\{-1,-2,-3,-6,-9,-18\}\\$
$2) x=\{1,2\}\\
3) x=\{1,2,3,6,-1,-2,-4,-6\}\\$
$4) x=-12\\
5) x=36$
Giải thích các bước giải:
1) $18\vdots x\Rightarrow x \in U(18)=\{-1,-2,-3,-6,-9,,-18,1,2,3,6,9,18\}$
Do $x<0 \Rightarrow x=\{-1,-2,-3,-6,-9,-18\}\\$
2) $2\vdots x\Rightarrow x \in U(2)=\{-1,1,-2,2\}$
Do $x>0\Rightarrow x=\{1,2\}\\$
$3) -18\vdots x,12\vdots x\Rightarrow x\in UCLN(18,12)\\
18=2.3^2\\
12=2^2.3\\
UCLN(12,18)=2.3=6\Rightarrow U(6)=\{1,2,3,6,-1,-2,-4,-6\}\\
\Rightarrow x=\{1,2,3,6,-1,-2,-4,-6\}\\
4) x\vdots 4,x\vdots -6\Rightarrow x\in BCNN(4,6)\\
4=2^2\\
6=2.3\\
BCNN(4,6)=2^2.3=12$
$\Rightarrow BC(12)=\{...,-36,-24,-12,0,12,24,36,...\}$
Do$-20<x<-10\Rightarrow x=-12\\
5) x\vdots 9,x\vdots -12\Rightarrow x \in BCNN(9,12)\\
9=3^2\\
12=2^2.3\\
BCNN(9;12)=2^2.3^2=36\Rightarrow B(36)=\{...,-36,0,36,72,...\}$
Do $20<x<50\Rightarrow x=36$
