Method 3: This method is the most complicated method and can only be used when we know two side lengths of a triangle as well as the measure of the angle that is between them. Grace is currently a math instructor at the City College of San Francisco and was previously in the Math Department at Saint Louis University. How do I find a perimeter of where sides a = 8.1, b = 16.1, c = 18 and height = 6? Then, you would take the square root of 25 to find c, which is 5. The simplest way to find the perimeter of a triangle is to add up the length of all of its sides, but if you don't know all of the side lengths you will need to calculate them first. Please help us continue to provide you with our trusted how-to guides and videos for free by whitelisting wikiHow on your ad blocker. In this example, the side lengths are each 5cm, so the correct value for the perimeter is 15cm. But remember that the perimeter formula is the same for any kind of triangle. ", "Thanks for helping someone learn how to do this work. This particular example is called an equilateral triangle, because all three sides are of equal length. Below table helps us to understand how to find the perimeter of different triangles- Equilateral triangle, Isosceles triangle and Scalene triangle. This was really helpful with an assignment. How can you find the missing side of a triangle given the perimeter? Finding the Perimeter When Three Side Lengths are Known, {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/3\/38\/Find-the-Perimeter-of-a-Triangle-Step-1-Version-2.jpg\/v4-460px-Find-the-Perimeter-of-a-Triangle-Step-1-Version-2.jpg","bigUrl":"\/images\/thumb\/3\/38\/Find-the-Perimeter-of-a-Triangle-Step-1-Version-2.jpg\/aid2157327-v4-728px-Find-the-Perimeter-of-a-Triangle-Step-1-Version-2.jpg","smallWidth":460,"smallHeight":345,"bigWidth":"728","bigHeight":"546","licensing":"