The lines with direction cosines l1, m1, n1 and l2, m2,n2 are perpendicular to each other if-
Answer & explanation
Correct answer: option 3
The lines with direction cosines l1, m1, n1 and l2, m2,n2 are perpendicular to each other if
l1.l2+ m1.m2+ n1.n2 = 0