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Across 1. Two angles whose sides form two pairs of opposite rays 5. A quadrilateral with four congruent sides 6. A statement that is accepted without proof 8. An example used to prove that an if-then statement is false 9. Two angles whose measures have the sum 180 15. Circles that lie in the same plane and have the same center 16. The figure formed by three segments joining three noncollinear points 17. Two angles in a plane that have a common vertex and a common side but no common interior points 18. A triangle with all angles congruent 19. A chord that contains the center of a circle 20. A line that contains a chord

Down 2. The perpendicular segment from a vertex to the line containing the opposite side 3. Two angles whose measures have the sum 90 4. A triangle with at least two sides congruent 7. A 10-sided polygon 10. A triangle with no sides congruent 11. A statement that contains the words "if and only if" 12. A segment whose endpoints lie on a circle 13. A statement that can be proved 14. A line that intersects two or more coplanar lines in different points