In this article, we’ll explore how to calculate the perimeter of a triangle, and we’ll illustrate this with some clear, step-by-step examples.

## The Formula for Calculating the Perimeter

The perimeter of a triangle is calculated by adding the lengths of all its sides.

If you have a triangle with sides of lengths * a*,

*, and*

**b***, the formula for its perimeter*

**c***is:*

**P***P = a + b + c*

So if the lengths of the sides of the triangle are known, you just have to add them together to find the perimeter.

### Perimeter of an Isosceles Triangle

An isosceles triangle is a type of triangle that has two sides of equal length, which we’ll call ‘* b*‘. The side that is different in length, referred to as ‘

*‘, is known as the base.*

**a**Therefore, the perimeter can be calculated as:

*P = a + 2b*

### Perimeter of an Equilateral Triangle

An equilateral, or regular triangle, is one where all sides are equal (let’s take it as ‘* a*‘).

The perimeter of such a shape is calculated as follows:

*P = 3a*

## Examples of Tasks

**Task 1**

Find the perimeter of a triangle if its sides are 3, 4, and 5 inches.

*Solution*

Substitute the known values from the task conditions into the formula and get:

*P = 3″ + 4″ + 5″ = 12″*

**Task 2**

Find the perimeter of an isosceles triangle if its base is 3 inches, and the side is 10 inches.

*Solution*

As we know, the sides of an isosceles triangle are equal, so:

*P = 3″ + 2 ⋅ 10″ = 23″*