Given circle x2+y2−4x−2y−4=0 Centre (2,1) Equation of diameter of circle passes through origin. x−2y=0 Equation of circle through the end point of diameter of circle and line x−2y=0 is x2+y2−4x−2y−4+λ(x−2y)=0 Since, this is passes through (1,2) ∵1+4−4−4−4+λ(−3)=0 λ=