Đáp án:
a) $x\in {-15,-9,-7,-1}$
b) $x \in {-5,1,3,9}$
Giải thích các bước giải:
a) $-7 \in B(x+8)\Rightarrow (x+8)\in U(-7)\\
U(-7)={-7,-1,1,7}\\
\Rightarrow x+8=-7\Rightarrow x=-15\\
x+8=-1\Rightarrow x=-9\\
x+8=7\Rightarrow x=-1\\
x+8=1\Rightarrow x=-7\\
x\in {-15,-9,-7,-1}$
b)
$(x-2) \in U(3x-13)\Rightarrow 3x-13 \vdots x-2\\
DK x-2\neq 0 \Leftrightarrow x\neq 2\\
3x-13=3(x-2)-7$
do $3x-13 \vdots x-2\Rightarrow [3(x-2)-7]\vdots x-2\\
\Rightarrow -7\vdots x-2\\
\Rightarrow(x-2) \in U(7)\\
U(7)={-7,-1,7,1}\\
\Rightarrow x-2=-7 \Leftrightarrow x=-5\\
x-2=-1 \Leftrightarrow x=1\\
x-2=7 \Leftrightarrow x=9\\
x-2=1 \Leftrightarrow x=3\\
x \in {-5,1,3,9}$
