Theory:

Now, we shall find the perimeter of an equilateral triangle.
 
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Let \(ABC\) be an equilateral triangle with sides of equal length \(s\) \(units\).
 
Then, the perimeter of the triangle \(ABC\) is given by:
Perimeter of the triangle \(=\) Product of \(3\) sides and its side length
Perimeter \(P = AB+BC+CA\) \(units\)

\(P = s+s+s\) \(units\)
 
\(P = 3s\) \(units\)
 
Therefore, the perimeter of an equilateral triangle is the product of \(3\) sides and the side length.
Example:
1. The side length of an equilateral triangle is \(9 \ cm\). Find the perimeter of an equilateral triangle.
 
Solution:
 
The side length of an equilateral triangle is \(s = 9\) \(cm\).
 
Perimeter \(= 3s\), where \(s\) is the length of three equal sides.
 
Substituting the value of \(s\) in the above formula, we have:
 
Perimeter \(= 3 \times 9\) \(cm\)
 
Perimeter \(= 27\) \(cm\)
 
Therefore, the perimeter of an equilateral triangle is \(27 \ cm\).