Circle: Center given, passing through a point: Find the equation of the circle with center at (4, -5) and passing through (2, -1).

With these conditions given, we can determine the radius by finding the distance between the center and the point on the circle. From the definition of distance, we get

We can now substitute into the equation of the circle with the coordinates of the center as h and k: h = 4, k = -5: