What is the perimeter of an equilateral triangle when each side is $ 13 $ cm?

Hint: Perimeter – It is the sum of all sides of the given polygon. In our case we are provided with an equilateral triangle. Equilateral triangle is a polygon with three sides which has all sides equal and every internal angle is equal to 60 degrees.

Complete step-by-step answer:
Given, it is an equilateral triangle
Side of the triangle is 13 cm
For calculating the perimeter of a triangle, we need to add the lengths of all sides. In this case the triangle given is an equilateral triangle.
Suppose $ a$ is the length of one side of equilateral triangle
$
  Perimeter = a + a + a \\
   \Rightarrow Perimeter = 3a \;
 $
The given data from the question, $ a = 13 cm$
Hence, perimeter of equilateral triangle
$
  Perimeter = 3a \\
   \Rightarrow Perimeter = 3(13) \\
   \Rightarrow Perimeter = 39 \;cm \;
 $
Therefore, by calculation we get the perimeter of an equilateral triangle of side $ a = 13\;cm\,is\,39\;cm$
So, the correct answer is “ $ 39 $ cm”.

Note: It is advised that students should know the difference between area and perimeter right away. After that the formulas for calculation of both area and perimeters must be known by students. These two things will help in developing accuracy and save time in examination.