The equations of the tangents drawn from the origin to the circle x2+y2−2rx−2hy+h2=0 , is

The combined equation of the pair of tangents drawn from  (x1, y1) to a circle S=0 is given by SS'=T 2 .So, the equations of the tangents drawn from (0, 0) to    x2+y2−2rx−2hy+h2=0a are given by h2x2+y2−2rx−2hy+h2=−xr−hy+h22⇒xh2−r2x−2rhy=0⇒x=0 or h2−r2x−2 rhy =0