
Directrix x+y=0
$\begin{aligned}
& \mathrm{PS}=\mathrm{PM} \
& \sqrt{(1-2)^2+(\mathrm{K}-2)^2}=\frac{(1+\mathrm{K})}{\sqrt{2}} \
& 2 \mathrm{K}^2+8-8 \mathrm{K}+2=\mathrm{K}^2+1+2 \mathrm{K} \
& \mathrm{K}^2-10 \mathrm{K}+9=0 \
& \mathrm{K}=9 \
& \text { option (2) }
\end{aligned}$