(1,2) is a point on L=0 and (2,-1) is a point on L'=0. If equation of the angular bisector is x-3y=0 find the equations of L=0 and L'=0.

Find the reflection of (1,2) about x – 3y=0, that point shall surely lie on L’. Thus 2 points on L’ will be known (as (2,-1) is already given) and we can write the eqn using 2 point form. Similarly Find the reflection of (2, – 1) about x – 3y=0, that point shall surely lie on L.