FORMULABANK

The point that is equidistant from all points on the circle's circumference. (Also known as the midpoint.)

The boundary of the circle. The distance from the circumference to the center is always the radius.

A portion of the circumference, defined by a central angle.

$\text{Arc length}=\frac{\mathrm{circumference}\cdot \mathrm{central}\mathrm{angle}}{360}$

The distance from the center to the circumference.

A chord that passes through the center. The diameter is 2 times the radius.

A sector is a portion of the circle's area, defined by a central angle.

$\text{Sector area}=\frac{\mathrm{area}\cdot \mathrm{central}\mathrm{angle}}{360}$

A line that touches the circle at exactly one point and is perpendicular to the radius at that point.

A straight line segment that connects two points on the circumference.

The area between an arc and a chord.

An angle whose vertex is at the center of the circle.

An angle whose vertex is on the circumference of the circle.
If an inscribed angle and a central angle share the same chord, then:

The inscribed angle is always half the size of the central angle when the inscribed angle lies outside the legs of the central angle.

If the inscribed angle lies between the legs of the central angle, the angle will always be:

$180-\frac{\mathrm{central}\mathrm{angle}}{2}=\mathrm{inscribed}\mathrm{angle}$