1. An angle that measures between 0 and 90 degrees.
Acute Angle

2. To cut in half.
Bisect

3. The point where the angle bisectors of a triangle meet.
Incenter

4. A polygon that is both equilateral and equiangular.
Regular Polygon

5. Objects that lie in the same plane.
Coplanar

6. Two angles whose measures add up to ninety degrees.
Complementary Angles

7. Two adjacent angles whose noncommon sides form opposite rays.
Linear Pair

8. A segment that connects the midpoints of two sides of a triangle.
Midsegment

9. A segment that connects a vertex of a triangle with the midpoint of the opposite side.
Median

10. A triangle with three congruent sides.
Equilateral/
Equiangular/Acute/
Regular/Isosceles

11. The distance around a figure.
Perimeter

12. A polygon with four congruent sides.
Equilateral Quadrilateral

13. Objects that have the same angle measures and the same side lengths.
Congruent Figures

14. Every point on the ______ is equidistant from the endpoints of the segment.
Perpendicular Bisector

15. The side of a right triangle opposite the right angle.
Hypotenuse

16. A point that divides a segment into two congruent segments.
Midpoint

17. c2 = a2 + b2.
The Pythagorean Theorem

18. Two angles whose measures add up to one hundred and eighty degrees.
Supplementary Angles

19. The angles adjacent to the base.
Base Angles

20. The angle in an isosceles triangle opposite the base.
Vertex Angle

21. Lines that intersect to form a right angle.
Perpendicular Lines

22. Points that lie on the same line.
Collinear Points

23. A non-rigid transformation.
Dilation

24. An educated guess based on observations.
Conjecture

25. The ratio of rise over run between two points on a coordinate plane.
Slope

26. The point of concurrency of the medians of a triangle.
Centroid

27. What you need to prove a conjecture is false.
Counterexample

28. A statement that is accepted without proof.
Postulate

29. A polygon that has no “dents”.
Convex Polygon

30. The point of concurrency of the altitudes in a triangle.
Orthocenter

31. The point of intersection of the perpendicular bisectors of a triangle.
Circumcenter

32. A polygon that has a dent.
Concave

33. A series of statements and reasons that explain why something is true.
Proof

34. A triangle with at least two congruent sides.
Isosceles Triangle

35. The words that follow “then” in a conditional statement.
Conclusion

36. A line that intersects two other lines at different points.
Transversal

37. A segment or line that goes from a vertex of a triangle to the opposite side or to a line that contains the opposite side and makes a right angle.
Altitude

38. Lines that do not intersect and are not coplanar.
Skew Lines

39. The words that follow “if” in a conditional statement.
Hypothesis

40. The two sides of a right triangle that form the right angle.
Legs of a right triangle

41. A statement that contains the phrase “if and only if.”
Biconditional statement

42. Coplanar lines that do not intersect.
Parallel Lines