Find an equation of the circle with center at the origin and passing through (2,-5) in the form of (x-A)^2+(y-B)^2=C where A,B,C are constant.

Answer 1

a circle centered at (h,k) with radius r has the general equation
... (x - h)^2 + (y - k)^2 = r^2

in this case ; h and k are zero (origin) , and ... r^2 = 2^2 + (-5)^2