# Introduction

To calculate the area of a triangle, we first need to understand how to calculate the area of a rectangle.

For example:

The area of this 3×5 rectangle is simply , if we suppose the dimensions have been given in meters.

The formula to calculate the area of a rectangle is

The area of the triangle of the same rectangle is half the area of the rectangle, i.e.:

So the formula for area of a triangle is

In this example, it would be

Even if the triangle is not a right-angled triangle, it is still half of a rectangle, i.e.:

So the formula is still

In the above example, it would be

Remember to use the Height though, and NOT the length of one of the sides!