Two-dimensional (2D) shapes are completely flat. They cannot be picked up. A polygon is a 2D shape with straight sides that meet at vertices. Polygons have names that show the number of sides they ...

Help sort shapes in a shape factory. Look at examples of shapes to see if they belong in a polygon group, or set. Examine examples of shapes that do not belong in the set. What features do you think ...

New work on the problem of “scissors congruence” explains when it’s possible to slice up one shape and reassemble it as another. If you have two flat paper shapes and a pair of scissors, can you cut ...