If the lines r = a_1 + b_1 ;and; r = a_2 + b_2 are coplanar then which of the following is correct ?
The trick is complete solution: write formula, plug data, do arithmetic. Final value matches ( a_2 - a_1 ) ( b_1 ; b_2 ) = 0. Simple and accurate.
Ref: NCERT Mathematics Class XII — Vectors and 3D Geometry
