If the center of the circle is to the right of the y-axis, C is negative and its absolute value increases as the center moves to the right. If the center is to the left of the y-axis, C is positive and its value decreases as the center moves to the right. D does not change when the center moves horizontally.
If the center of the circle is above the x-axis, D is negative and its absolute value increases as the center moves up. If the center is below the y-axis, D is positive and its value decreases as the center moves up. C does not change when the center moves vertically.
The values of C and D are not affected when the radius changes, as long as the center stays the same.
The other form of circle equation is (x-a)2 + (y-b)2 = r2. a and b is the coordinate of the center and r is radius. So the equation is x2+(y-4)2=9. Change it to the general form is x2+y2-8y+7=0. So A=1, B=1, C=0, D=-8 and E=7.
