5:
a: =>6 chia hết cho x
=>\(x\in\left\{1;2;3;6\right\}\)
b: =>x+1+8 chia hết cho x+1
=>8 chia hết cho x+1
=>\(x+1\in\left\{1;2;4;8\right\}\)
=>\(x\in\left\{0;1;3;7\right\}\)
c: =>2x-2+3 chia hết cho x-1
=>\(x-1\in\left\{1;-1;3\right\}\)
=>\(x\in\left\{2;0;4\right\}\)