) be a point on the line 4x−5y=20. Then the chord of contact of tangents drawn from P to the circle x2+y2=9 is tx(4t−
20
5
)y=9...(i) Let θ(h,k) be the mid-point of this chord of contact, then its equation is also hx+ky=h2+k2...(ii) Clearly Eqs. (i) and (ii) represent the same line ∴