Every circle has 5 types of angles:
1.Central angle - the angle formed by two radii with the vertex at the center of the circle.
Congruent central angles have congruent arcs and congruent central angles have congruent chords.
2. Inscribed angle - the angle with its vertex "on" the circle, formed by two intersecting chords.
Inscribed angles that intercept the same arc are congruent.Opposite angles in a cyclic quadrilateral are supplementary.
3. Tangent chord angle - angle formed by an intersecting tangent and chord.
4. Angle formed by two Intersecting chords
5. Angle formed outside of circle by intersection.
Arc is the connected section of the circumference of a circle. It can be measured as the central angle, or as the length of the arc itself.