Question 687664
The distance from a point (x,y) on the circle, and the center (2,3) is 4, so
{{{(x-2)^2+(y-3)^2=4^2}}}
{{{drawing(300,300,-1,8,-1,8,
grid(0),
circle(2,3,4),circle(2,3,0.1),
locate (2,3,"(2,3)"),circle(5,3+sqrt(7),0.1),
locate (5,3+sqrt(7),"(x,y)"),
line(2,3,6,3),line(5,3,5,3+sqrt(7)),
line(2,3,5,3+sqrt(7)),rectangle(5,3,5.2,3.2),
arrow(3.5,2.5,2,2.5),arrow(3.5,2.5,5,2.5),locate(3,2.5,x-2),
arrow(6.5,4.32,6.5,3),arrow(6.5,4.32,6.5,5.646),locate(6.6,4.8,y-3)
)}}}
{{{(x-2)^2+(y-3)^2=4^2}}} --> {{{x^2-4x+4+y^2-6y+9=16}}} --> {{{x^2+y^2-4x-6y+4+9=16}}} --> {{{x^2+y^2-4x-6y+4+9-16=0}}} --> {{{highlight(x^2+y^2-4x-6y-3=0)
}}}