Đáp án:
Vì $UCLN(a;b)=18$
$→a;b$ có dạng $18x;18y$
$→18x+18y=162$
$→x+y=\dfrac{162}{18}=9$
mà $(x;y)=1$
\[\to \left[ \begin{array}{l}\left\{\begin{matrix} x=1 & \\ y=8 & \end{matrix}\right.\to \left\{\begin{matrix} a=18& \\ b=18.8=144 & \end{matrix}\right. va \quad nguoc \quad lai \\\left\{\begin{matrix} x=4& \\ y=5 & \end{matrix}\right.\to \left\{\begin{matrix} a=4\times 18=72& \\ b=5\times 18=90 & \end{matrix}\right. va \quad nguoc \quad lai\\\left\{\begin{matrix} x=2& \\ y=7 & \end{matrix}\right.\to \left\{\begin{matrix} a=2\times 18=36& \\ b=7\times 18 =126& \end{matrix}\right. va \quad nguoc \quad lai\end{array} \right.\]
