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