equation of circle, x^2 + y^2 +2gx+2fy+c=0
You can clearly see the graph of a circle with the equation x^2 + y^2 +2gx+2fy+c=0 in red color. If we change the values of f, g and c using their corresponding slide bars we will see that the position and size of the circle will change. Let us observe how the size and position of the circle changes as we change the values of f, g and c.
Questions to think about Compare the coordinates of center with g and f, what do you observe? And how? Calculate √(g^2+f^2-c) and compare it with the radius of the circle, what do you observe?