Centre-Radius Form

Centre-Radius Form: Centre at (h, k)

Now let the centre be any point $C(h,k)$, not necessarily the origin, and let the radius still be $r$. Let $P(x,y)$ be any point on the circle, so

By the distance formula between $C(h,k)$ and $P(x,y)$:

Since $CP=r$,

$(x-h)^2+(y-k)^2=r^2$ …