$\Rightarrow 2 \mathrm{~b}=\mathrm{a}+\mathrm{c} \Rightarrow \mathrm{a}-2 \mathrm{~b}+\mathrm{c}=0$
$\therefore \mathrm{ax}+\mathrm{by}+\mathrm{c}$ passes through fixed point $(1,-2)$
$\therefore \mathrm{P}=(1,-2)$
For infinite solution,
$\mathrm{D}=\mathrm{D}_1=\mathrm{D}_2=\mathrm{D}_3=0$
$\mathrm{D}:\left|\begin{array}{lll}1 & 1 & 1 \\ 2 & 5 & \alpha \\ 1 & 2 & 3\end{array}\right|=0$
$\Rightarrow \alpha=8$
$D_1:\left|\begin{array}{lll}6 & 1 & 1 \\ \beta & 5 & \alpha \\ 4 & 2 & 3\end{array}\right|=0 \Rightarrow \beta=6$
$ \therefore Q=(8,6) $
$ \therefore P Q^2=113$