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 describe the unit circle. How to draw the unit circle and label its parts. How to strategize about finding coordinates on the unit circle.
How to identify a segment from the vertex angle in an isosceles triangle to the opposite side.
How to find the length of tangent segments drawn to a circle from the same point.
How to define arc length and how it is different from arc measure; how to calculate the length of an arc.