An infinite number of tangents can be drawn from (1, 2) to the circle x2+y2−2x−4y+λ=0, then λ=
5
Clearly the point (1, 2) is the centre of the given circle and infinite tangents can only be drawn on a point circle. Hence radius should be 0.
∴ √12+22−λ=0 ⇒ λ=5.