1/ $27\vdots x$
$\to x\in Ư(27)=\{\pm 1; \pm 3; \pm 9\; pm 27\}$
mà $x\in N$
$\to x=\{1;3;9;27\}$
2/ $4\vdots x-1$
$\to x-1\in Ư(4)=\{\pm 1;\pm 2;\pm 4\}$
$\to$ Bảng giá trị.
$\begin{array}{|c|c|c|}\hline x-1&1&-1&2&-2&4&-4\\\hline x&2&0&3&-1&5&-3\\\hline\end{array}$
mà $x\in N$
$\to x=\{2;0;3;5\}$
3/ $5\vdots x+1$
$\to x+1\in Ư(5)=\{\pm 1;\pm 5\}$
$\to$ Bảng giá trị.
$\begin{array}{|c|c|c|}\hline x+1&1&-1&5&-5\\\hline x&0&-2&4&-6\\\hline\end{array}$
mà $x\in N$
$\to x=\{0;4\}$
4/ $7\vdots x+1$
$\to x+1\in Ư(7)=\{\pm 1;\pm 7\}$
$\to$ Bảng giá trị.
$\begin{array}{|c|c|c|}\hline x+1&1&-1&7&-7\\\hline x&0&-2&6&-8\\\hline\end{array}$
mà $x\in N$
$\to x=\{0;6\}$
5/ $x+2\vdots x+1$
$\to (x+1)+1\vdots x+1$
$\to 1\vdots x+1$
$\to x+1\in Ư(1)=\{pm 1\}$
$\to$ Bảng giá trị.
$\begin{array}{|c|c|c|}\hline x+1&1&-1\\\hline x&0&-2\\\hline\end{array}$
mà $x\in N$
$\to x=\{0\}$
