first we will write different type of equation for circle so we can see how did we get coeficients C D and E
(x-x1)^2 + (y-y1)^2 = r^2
where x,y is coordinate of a point on circle, x1,y1 are coordinates of the center of circle and r is radius of circle
after solving binomials on square we get terms like this:
-2xx1 and -2yy1
looking at like term in our given equation we can conclude that there is no "r" in those terms meaning that changing radius doesnt depend on coefficients C and D. They depend only on coordinates of the center of circle.
As for coefficient E.
if we move r^2 to left side we can see that E = x1^2 + y1^2 -r^2 meaning that if we decrease "r", E will increase.
