
DR's of Line L≡−1:1:2 DR's of AB≡α−2:β−2:γ−2 $\begin{aligned}
& \mathrm{AB} \perp_{\mathrm{ar}} \mathrm{L} \Rightarrow 2-\alpha+\beta-2+2 \gamma-4=0 \
& 2 \gamma+\beta-\alpha=4
\end{aligned}$
Let C is mid-point of AB $\begin{aligned}
& \mathrm{C}\left(\frac{\alpha+2}{2}, \frac{\beta+2}{2}, \frac{\gamma+2}{2}\right) \
& \text { DR's of PC }=\frac{\alpha}{2}: \frac{\beta-2}{2}: \frac{\gamma}{2} \
& \text { line L } \left\lvert, \mathrm{PC} \Rightarrow \frac{-\alpha}{2}=\frac{\beta-2}{2}=\frac{\gamma}{4}=\mathrm{K}(\text { let) }\right.
\end{aligned}\begin{aligned}
& \alpha=-2 \mathrm{K} \
& \beta=2 \mathrm{K}+2 \
& \gamma=4 \mathrm{K}
\end{aligned}usein(1)\Rightarrow K=\frac{1}{6}valueof\alpha+\beta+6 \gamma=24 \mathrm{K}+2=6$