Question

The radical axis of the circles, belonging to the coaxal system of circles whose limiting points are (1, 3) and (2, 6), is
A. `x-3y-15=0`
B. `x+3y-15=0`
C. `x-3y+15=0`
D. `2x+3y-15=0`

Answer 1

Correct Answer - B
We know that the limiting points are circles of the coaxial system with zero radius. The equations of the point circles having (1, 3) and (2, 6) as limiting points are
`S_(1)=(x-1)^(2)+(y-3)^(2)=0` ...(i)
and, `S_(2)=(x-2)^(2)+(y-6)^(2)=0` ...(ii)
The equation of their radical axis is
`S_(1)-S_(2)=0 rArr x+3y-15=0`.