Question

If(4,-2) is a point on the circle x┬▓+ y┬▓ + 2gx+ 2fy + c = 0 which is concentric to the x┬▓+ y - 2x + 4y+ 20 =0 then the value of c is

Answer 1

Hey mate
here's the solution
as it is concentric So center of both circles are same

-g ,-f = 1,-2

g = -1
f=2

hence x^2 + y^2 -2x + 4 y + c= 0 it becomes

now (4,-2) lies on this

16 + 4 -8 -8 + c=0

c= -4