# Area of an Isosceles Triangle

The **area of an isosceles triangle** is calculated from the base *b* (the non-repeated side) and the height (*h*) of triangle corresponding to the base. The area is the product of the base and the altitude divided by two, being its **formula** the following one:

## How is it obtained?

The area of **isosceles triangle** is obtained as the base product (side *b*) by height (*h*) divided by two (*Note*: *why is the **area of a triangle half of the base product by height?*).

This can be calculated from Pythagorean theorem. The sides *a*, *b/2* and *h* form a right angled triangle. The sides *b/2* and *h* are the legs and *a* the hypotenuse.

The **altitude** *h* corresponding to the base is obtained by the following calculations:

The **height** (altitude) (*h*) will be:

It is applied that **area** is a half of the multiplication of **base** (*b*) by **height** (*h*):

The **formula**of ** area** of isosceles triangle is reached.

Download this **calculator** to get the results of the formulas on this page. Choose the initial data and enter it in the upper left box. For results, press ENTER.

Triangle-total.rar or Triangle-total.exe

Note. Courtesy of the author: **José María Pareja Marcano**. Chemist. Seville, Spain.

## Exercise

Determine the **area** of a isosceles triangle knowing its two equal sides (*a*=3 cm) and the unequal one, whose length is 2 cm (*b*=2 cm).

What is its **area**?

Calculate the area using the above formula by multiplying the base by the height:

The **area** of this isosceles triangle is **2.83 cm ^{2}**.

## Table of Triangle Area Formulas

You can see the **table of triangle area formulas **. Depending on the type of triangle you may need one element ( equilateral triangle), two (base and height) or three (as long as they are not the three angles).