Goi A(x;y). ta co:$\overrightarrow{PA}$=(x;y+4)
$\overrightarrow{MN}$=(1;2)Ta co tu giac APMN la hinh binh hanh$\Rightarrow$ $\overrightarrow{PA}$=$\overrightarrow{MN}$$\Leftrightarrow$$\left\{ \begin{array}{l} x=1\\ y+4=2 \end{array} \right.$
$\Leftrightarrow$$\left\{ \begin{array}{l} x=1\\ y=-2 \end{array} \right.$
Vay A(1;-2)