Let (x1,y1) be any point on the circle x2+y2=r2 Then, x12+y12=r12 ...(i) Equation of chord of contact of tangents from (x1,y1) to the circle x2+y2=r22 is xx1+yy1=r22 ...(ii) ∵ Eq. (ii) touches the circle x2+y2=r32 The length of perpendicular from centre (0,0) on Eq. (ii) is radius =r3 ⇒