# 2D polygons

## Elementary geometry in 2 dimensions

### Triangles

#### Area of a triangle

#### Circumference of a triangle

#### Sum of angles of a triangle

Angles in a triangle add to \(\pi \).

### Quadrilaterals

### Oblongs

#### Area of an oblong

#### Circumference of an oblong

### Squares

#### Area of a square

\(A=r^2\)

#### Circumference of a square

\(C=2r\)

#### Angles in a square

Angles in a square sum to \(2\pi \).

### Pentagon