Before you read this article you must know,
What is Perimeter
Perimeter of Equilateral Triangle is to sum of length of all its sides
So, Perimeter of Equilateral Triangle = side + side + side
We know that in Equilateral Triangle all sides are equal, so we get;
Perimeter of Equilateral Triangle = 3 side
P = 3s
Example 1  In the following equilateral triangle
Perimeter of Equilateral Triangle = 3 s
P = 3 * 3
P = 9cm
Example 2  In the following equilateral triangle
Perimeter of Equilateral Triangle = 3 s
P = 3 * 5
P = 15 cm

