# Perimeter of an Isosceles Triangle

The **perimeter of an isosceles triangle** is obtained as the addition of the three sides of the triangle. Having two equal sides, the perimeter is twice the repeated side (*a*) plus the different side (*b*).

In an isosceles triangle, if the repeating side (*a*) and the angle they form are known, the other side (*b*) should be found by **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

Being an **isosceles triangle** with two equal sides, *a*=3 cm and a different side of *b*=2 cm.

What is its **perimeter**?

To calculate this **perimeter** we add the repeated side multiplied by two plus the unequal side, i.e.:

It is obtained that the isosceles triangle’s **perimeter** is **8 cm**.

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A common error is to assume that a triangle that has a fixed perimeter must also have a fixed area. This is definitely

Right