1. Go Math Grade 3 Chapter 12 Two-Dimensional Shapes
Developing Math Language
Grade 3
Lori Hyland

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
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. Open shape A shape that does not begin and end at the same point.
Examples:
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. line of symmetry
An imaginary line on a figure that when the figure is folded on this line, the two parts match exactly. Example :