Perimeter of an Isosceles Triangle

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Drawing of the isosceles triangle for calculating its perimeter

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).

Formula of the perimeter of an isosceles triangle

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).

Drawing of the isosceles triangle for the calculation of its perimeter by the law of cosines

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

Example of isosceles triangle for calculating its perimeter

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.:

Example of calculating the perimeter of an isosceles triangle

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


AUTHOR: Bernat Requena Serra

YEAR: 2018


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3 Responses

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  2. Aformations says:

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

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