How to define a chord; how to describe the effect of a perpendicular bisector of a chord and the distance from the center of the circle.
How to prove that an angle inscribed in a semicircle is a right angle; how to solve for arcs and angles formed by a chord drawn to a point of tangency.
How to define a central angle and find the measure of its intercepted arc; how to describe the intercepted arcs of congruent chords.
How to define a secant; how to find the length of various secants in circles.
How to define a circle and identify its main parts.