Develop and use precise definitions of figures such as angle, circle, perpendicular lines, parallel lines, and line segment, based on the undefined notions of point, line, distance along a line, and distance around a circular arc.

Example Problems
The diameter of a circle is units.
What is the
radius of the circle?
The radius of a circle is .
What is the
diameter of the circle?
The radius of a circle is . What is the diameter of the circle?
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