If the tangents from (1,1) to the circle x2+y2−4x+k = 0 are pendicular then k =
0
3
x2+y2−4x+k = 0 θ = 90o ∴r = √S11
⇒√4−k = √1+1−4+k
⇒4−k = k−2
⇒2k = 6 ⇒k=3