Chapter 14 Developing Geometric Thinking and Spatial Sense

2. one whose interior angles are all less than 180°; that is, any two points in a figure can be connected by a line segment that will be completely within the figure and all diagonals will remain inside the figure.
4. the study of the properties of figures that stay the same even under distortions, except tearing or cutting.
7. A nonconvex polygonal region
9. the movement of a figure about a line outside the figure, on a side of the figure, or intersecting with a vertex.
11. the points where edges of the shape meet
12. a flat region being covered with repetitions of the same figure without any overlapping.

1. a seven-piece puzzle consisting of five triangles (2 large, 1 medium, and 2 small), one square, and one parallelogram cut from a square. These parts can be arranged to create different shapes, such as a rectangle, a large triangle, a boat, or a building.
3. two-dimensional figures with straight-line segments.
5. a movement along a straight line
6. a foundational subject to many other areas of mathematics, such as algebraic thinking involving patterns and problem-solving activities involving area and perimeter of geometric shapes. It also is about developing spatial sense—the ability to build and manipulate mental representations of two-and three-dimensional objects and perceive them accurately from different perspectives
8. three-dimensional shapes with faces consisting of polygons
10. changing an object. They can be achieved by twisting, bending, stretching, and shrinking