Given: L1⊥L2
⇒(i^−j^+2k^).(3i^+j^+pk^)=0
⇒3−1+2p=0
⇒p=−1
Also, L3⊥L1,L2
So, L3∥(L1×L2)
⇒L1×L2=∣i^13j^−11k^2−1∣
⇒L1×L2=−i^+7j^+4k^
On comparing with L3:r=δ(li^+mj^+nk^), we get that (−δ,7δ,4δ) will lie on L3.
Now, for δ=1 the point will be (−1,7,4).