2D Geometry
Polygon  a closed, 2D shape made of at least 3 straight lines.
Sides  the edges of a polygon. The number of shapes determines the name of the polygon.
Angles  the inside corner where two straight lines meet.
Vertex/Vertices  the outside corner where two straight lines meet. A polygon will always have the same number of angles and vertices.
You can play with different polygons on this website.


Triangles
All triangles have 3 sides, 3 angles, and 3 vertices. The sum of all of the angles within a triangle will always be 180 degrees. You can identify triangles by their side lengths and angles.
Play with interactive triangles here
Visit http://wonderopolis.org/wonder/howmanytypesoftrianglesarethere to read all about triangles on Wonderopolis.
Quadrilaterals
All quadrilaterals are 4 sided polygons. A quadrilateral will always have 4 sides, 4 angles, and 4 vertices. The inside angles of a quadrilateral will always add up to 360 degrees,
We can classify quadrilaterals by putting them into a hierarchy. Use the image below to help you describe the relationships between quadrilaterals. Quadrilaterals can be grouped into two main groups: parallelograms and nonparallelograms. From there, the quadrilaterals have specific characteristics that make them specific traits.
We can classify quadrilaterals by putting them into a hierarchy. Use the image below to help you describe the relationships between quadrilaterals. Quadrilaterals can be grouped into two main groups: parallelograms and nonparallelograms. From there, the quadrilaterals have specific characteristics that make them specific traits.