# Perimeter of a Scalene Triangle

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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.

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.

AUTHOR: Bernat Requena Serra

YEAR: 2020