# Geometry Formulas

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### How to Calculate the Area of a Parallelogram, Kite, or Trapezoid

The area formulas for the parallelogram, kite, and trapezoid are based on the area of a rectangle. The following figures show you how each of these three quadrilaterals relates to a rectangle, and the

### A Rhombus Area Problem

Here’s a rhombus area problem involving triangles and ratios: Find the area of rhombus RHOM given that MBis 6 and that the ratio of RB to BH is 4 : 1, as shown in the following figure.

### How to Calculate the Area of a Kite

You calculate the area of a kite by using the lengths of its diagonals. Here’s an example: what’s the area of kite KITE in the following figure?

### How to Calculate the Area of a Trapezoid

You can use the right-triangle trick to find the area of a trapezoid. The following trapezoid TRAP looks like an isosceles trapezoid, doesn’t it? Don’t forget — looks can be deceiving.

### How to Calculate the Area of a Regular Octagon

You can calculate the area of a regular octagon with the standard regular polygon method, but there’s a nifty alternative method based on the fact that a regular octagon is a square with its four corners

### Interior and Exterior Angles of a Polygon

Everything you need to know about a polygon doesn’t necessarily fall within its sides. You may need to find exterior angles as well as interior angles when working with polygons:

### How to Find the Number of Diagonals in a Polygon

To find the number of diagonals in a polygon with nsides, use the following formula:

### How to Calculate the Area of a Quadrilateral

There are five formulas that you can use to calculate the area of the seven special quadrilaterals. There are only five formulas because some of them do double duty — for example, you can calculate the

### How to Calculate the Area of a Regular Polygon

A regular polygon is equilateral (it has equal sides) and equiangular (it has equal angles). To find the area of a regular polygon, you use an apothem — a segment that joins the polygon’s center to the

### How to Calculate the Area of a Regular Hexagon

One way to find the area of a regular hexagon is by first dividing it into equilateral triangles. You also need to use an apothem — a segment that joins a regular polygon’s center to the midpoint of any