Đáp án: $x\in\{-2,-1,-4,-5\}$
Giải thích các bước giải:
Ta có:
$(3x+11)\quad\vdots\quad x+3$
$\to (3x+9)+2\quad\vdots\quad x+3$
$\to 3(x+3)+2\quad\vdots\quad x+3$
$\to 2\quad\vdots\quad x+3$
Mà $x\in Z\to x+3\in Z$
$\to x+3\in U(2)$
$\to x+3\in\{1,2,-1,-2\}$
$\to x\in\{-2,-1,-4,-5\}$