# Perimeter of a Scalene Triangle

A scalene triangle is a triangle in which all three sides are in different lengths. The **perimeter of a scalene triangle** with three unequal sides is determined by adding the three sides.

If you know the length of the three sides, it’s easy to calculate its perimeter using the following formula:

If you know two sides of the triangle and the angle they form you can solve for the missing side using the Law of Cosines (Cosine Rule):

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 1

Consider a given triangle:

Let be a **scalene triangle** of known sides, these being *a*=2 cm, *b*=4 cm and *c*=3 cm.

What is its **perimeter**? This will be calculated as the sum of its three sides.

So, the **perimeter** is **9 cm**.

## Exercise 2

What is its perimeter?

**Solution:**

In this triangle we only know two sides (*a*=4 cm y *c*=6 cm) and the angle they form (B=85°). First we have to find the length of side *b*.

For this we use the Law of Cosines:

So, we get the side *b*=6.92 cm.

Now we can calculate the perimeter by adding the three sides of the triangle:

The perimeter of the triangle is **16.92 cm**.