D s 2 arcsin C 2. Half of the diameter or the distance from the midpoint to the circle border is called the radius of the circle r. According to the distance formula this is sqrt x-02 y-02sqrt x2y2 A point x y is at a distance r from the origin if and only if 133 x 2 y 2 r or if we square both sides.
Therefore the equation of the circle with centre h k and the radius a is x-h 2 y-k 2 a 2.
For example it can be equal to 15 cm. It is denoted by C in math formulas and has units of distance such as millimeters centimeters meters or inches. The equation of a circle with center h k and radius r units is x h 2 y k 2 r 2. Half of the diameter or the distance from the midpoint to the circle border is called the radius of the circle r.