Let the tangents drawn from the origin to the circle, x2+y2−8x−4y+16=0 touch it at the points A and B. Then AB2 is equal to:

Length of tangent=L=S1=16=4Radius of the circle=R=16+4−16=2∴Length of Chord of contact =2LRL2+R2=2×4×216+4=1620⇒Square of length of chord of contact =645