The correct option is B √135
Given lines are L1:x−1−1=y+12=z−11 and L2:x−11=y+1−1=z−12
D.R′s of L1=(−1,2,1)
⇒D.c′s=(−1√6,2√6,1√6)
D.R′s of L2=(1,−1,2)
⇒D.c′s=(1√6,−1√6,2√6)
Here l1.l2+m1.m2+n1.n2=−16−26+26=−16<0
∴ Obtuse angle bisector D.R′s will be (l1+l2,m1+m2,n1+n2) i.e (0,1,3)
∴ Obtuse angle bisector equation is
x−10=y+11=z−13
Now, let x−10=y+11=z−13=t
⇒P(x,y,z)=(1,t−1,3t+1)
∴1.0+(t−1).1+(3t+1).3=0
⇒10t=−2⇒t=−15
∴P=(1,−65,25)
So, we have −−→OP=√1+3625+425=√135