Question

formula of pair of tangents

Answer 1

Given a circle C(x,y)≡x2+y2+2gx+2fy+c=0C(x,y)≡x2+y2+2gx+2fy+c=0 and a point P=(x1,y1)P=(x1,y1) outside the circle, the equation of the pair of straight lines that are tangent to the circle and pass through PP is given by

C(x1,y1)C(x,y)=T(x,y)2,C(x1,y1)C(x,y)=T(x,y)2,

where T(x,y)T(x,y) is the equation of the chord of contact of the tangents drawn from point PP.