2. plane shape A shape in a plane that is formed by curves, line segments, or both. These are some plane figures 12.1

3. An exact position or location. point 12.1

4. line A straight path extending in both directions with no endpoints Example: 12.1

5. endpoints Points that are used to show segments of lines. Example: 12.1

6. line segment A part of a line that includes two points, called endpoints, and all the points between them Example: 12.1

7. ray A part of a line, with one endpoint, that is straight and continues in one direction. Example: 12.1

8. two-dimensional shape A shape that lies in a plane; a shape having length and width. Example: 12.1

9. closed shape A shape that begins and ends at the same point. Examples: 12.1

10. A shape that does not begin and end at the same point. Examples: Open shape 12.1

11. angle A figure formed by two rays or line segments that share an endpoint. Example: 12.2

12. vertex The point at which two rays of an angle or two (or more) line segments meet in a plane figure or where three or more edges meet in a solid figure Example: 12.2

13. right angle An angle that forms a square corner Example: 12.2

14. acute angle An angle that has a measure less than a right angle. Example:

15. obtuse angle An angle that has a measure greater than a right angle. Example

16. straight angle An angle in which two rays point in opposite directions so that they form a line Example:

17. polygon A closed plane figure with straight sides that are line segments. Examples: 12.3

18. side a line segment of a polygon Example: This polygon has 4 sides 12.3

19. triangle A polygon with three sides and three angles. Examples: 12.3

20. quadrilateral A polygon with four sides and four angles. Example: 12.3

21. pentagon A polygon with five sides and five angles. Examples: 12.3

22. hexagon A polygon with six sides. Examples: 12.3

23. octagon A polygon with eight sides and eight angles. Examples : 12.3

24. Decagon A polygon with ten sides and ten angles. Example: 12.3

25. intersecting lines lines that cross Example: 12.4

26. perpendicular lines Lines that intersect to form right angles. Example: 12.4

27. parallel lines Lines that never cross; lines that are always the same distance apart. Example: 12.4

28. parallelogram A quadrilateral whose opposite sides are parallel and have the same length. Example :

29. trapezoid A quadrilateral with exactly one pair of parallel sides and four angles. Example:

30. rectangle A quadrilateral with 2 pairs of parallel sides, 2 pairs of equal sides, and 4 right angles. Example: 12.5

31. square A quadrilateral with 2 pairs of parallel sides, 4 equal sides, and 4 right angles. Example: 12.5

32. rhombus A quadrilateral with 2 pairs of parallel sides and 4 equal sides and four angles. Example: 12.5

33. equilateral triangle A triangle that has three equal sides and three equal angles. Examples:

34. isosceles triangle A triangle that has two equal sides. Example:

35. scalene triangle A triangle in which no sides are equal Example:

36. right triangle A triangle with one right angle Example:

37. obtuse triangle A triangle that has 1 obtuse angle. Example:

38. acute triangle A triangle that has three acute angles. Example:

39. Venn Diagram A diagram that shows relationships among sets of things. 12.8

40. diagonal A line segment that connects two vertices of a polygon that are not next to each other Example:

41. congruent Figures that have the same size and shape. Example:

42. symmetry A figure has symmetry if it can be folded along a line so that the two parts match exactly; one half of the figure looks like the mirror image of the other half. Example: line of symmetry

43. An imaginary line on a figure that when the figure is folded on this line, the two parts match exactly. Example :