How can I find the area of a equilateral triangle (3 sides) given only one of it's side lengths.
To find the area of an equilateral triangle with one known side length, you can use the following formula:

Area = (sqrt(3) / 4) x s^2

where s is the length of one side of the equilateral triangle.

So, if you are given a side length of s, you can plug it into the formula and solve for the area.
How about if that side is 15 cm long?
You can calculate the area as:
Area = sqrt(3) / 4 * (15 cm)² = 97.43 cm²
rounded to the second digit
If the object instead has 4 sides with the same angle in the corners. The side length is still 15 cm long. What is the area?