# Two-Dimensional Shapes

What is 2-D? We mean**two-dimensional**. Aaaand... What is that? A 2-D object is an object with no

**depth**. The closest you will ever come to seeing one is a paper cutout of a shape. But even that paper has a very small thickness, so it is truly 3-D. You might also hear the word

**polygon**. That's another name for a 2D object. We're going to give you a little overview of the polygons you may see in your math travels.

# Triangles

A triangle is the generic name for a shape with three (3) sides. There are different types of triangles. You might hear about an equilateral triangle. That is a triangle with all three of its sides at equal lengths. Another type is an isosceles triangle. That a triangle with two (2) sides of equal length and the third side is different.# Quadrilaterals and Squares

A quadrilateral is a shape with four (4) sides. You might hear about squares, rectangles, a rhombus, or a trapezoid. These are all different types of quadrilaterals. Squares have all sides with equal lengths and right angles (90 degree angles). A rhombus is really close to a square, bit it's at a tilt so that there are no right angles. It is like a diamond on its side.# Pentagons and Hexagons

Moving up in the number of sides we find pentagons with five (5) sides. Next in the number of sides, we discover hexagons. Hexagons have six (6) sides. You can add even more sides to polygons. There is no limit. We're also doing something different with these pics. You should know that a**polygon**could be any shape, even all bent and funny. If all of your sides have equal lengths, you are a regular polygon.

# Ellipses and Circles

What happens if you only have one side? Is that possible? Kind of. Ellipses are circular shapes that could be circles or ovals. The border goes all the way around and there are no corners. You could also think about it as a polygon with an infinite amount of sides that all blend together.# Other Shapes

You will find other types of shapes in the math world. Cardioids are like circles with a dimple on one side. A good example of a cardioid is a heart shape. You will also find stars. Typical star shapes are the five-pointed kind. Stars are created by connecting the corners of shapes with more than four sides. The list goes on, but not on this page.## Related Activities

Two-Dimensional Shape Name Quiz
- Play Activity |
Two-Dimensional Shape Memory Challenge
- Play Activity |

# Useful Reference Materials

**Wikipedia:**

*https://en.wikipedia.org/wiki/Pre-algebra*

**Encyclopædia Britannica:**

*http://www.britannica.com/topic/mathematics*

**College of the Redwoods:**

*http://mathrev.redwoods.edu/PreAlgText/*