Fill in the blanks with the appropriate word, phrase, or symbol(s) from the following list.
$\text { distance } \quad \text { (0,0) } \quad \text { parabola } \quad \text { circle } \quad \text { (k, h)}\quad \text { (h, k) } \quad \text { (x, y)} \quad \text { midpoint}$
The equation $(x-h)^{2}+(y-k)^{2}=r^{2}$ is the equation of a circle with center at _______ and radius $r$.