match the following vocabulary 1. a portion of the circumference of a circle circumference 2. an arc which measures exactly 180° arc length 3. an arc which measures less than 180° radius 4. the degree measurement of an arc (in reference to its central angle) arc measure 5. the distance around a circle diameter 6. the distance through the center between points on a circle minor arc 7. the distance from the center to any point on a circle semicircle