Question

An infinite number of tangents can be drawn from (1, 2) to the circle $x^2+y^2-2x-4y+\lambda =0,$ then $\lambda =$

• A. -20
• B. 0
• C. 5
• D. Cannot be determined

Answer 1

The correct option is C

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.
$\therefore \sqrt{1^2+2^2-\lambda }=0\Rightarrow \lambda =5.$