Geometry

1. The perpendicular segment from a vertex to the line containing the opposite side.
5. A 5-sided polygon.
6. The figure formed by three segments joining three non collinear points. Each of the three points is a vertex of the triangle and the segments are the sides.
7. A segment from a vertex to the midpoint of the opposite side.
8. A 4-sided polygon.
12. A segment whose endpoints lie on a circle.
14. An example used to prove that an if-then statement is false. For that counterexample, the hypothesis is true and the conclusion is false.
15. Two angles in a plane that have a common vertex and a common side but no common interior points.
16. A segment joining two non-consecutive vertices of a polygon.
17. A plane figure formed by coplanar segments such that each segment intersects exactly two other segments, one at each endpoint; and no two segments with a common endpoint are collinear.
18. Lines that are not coplanar.

2. A line that intersects two or more coplanar lines in different points.
3. A 10-sided polygon.
4. An angle with measure between 0 and 90.
9. A quadrilateral with four congruent sides.
10. A quadrilateral with four right angles and four congruent sides.
11. Two angles whose sides form two pairs of opposite rays.
12. The set of points in a plane that are a given distance from a given point in the plane. The given point is the center, and the given distance is the radius.
13. A quadrilateral with four right angles.
15. A figure formed by two rays that have the same endpoint. The two rays are called sides of the angle. Their common endpoint is the vertex.