The equation of a circle in standard form:
(h, k) - center
r - radius
The center is a midpoint of MN. The formula of a midpoint:
We have M(2, 4) and N(9, 4). Substitute:
Therefore we have the center (5.5, 4) → h = 5.5 and k = 4.
The radius of a distance between the center and M.
The formula of a distance between two points:
We have the points (5.5, 4) and (2, 4) Substitute:
Substitute to the equation of a circle: