There are two ways to calculate the area of a decagon. The first only needs the side length. The second also uses the apothem.
When you only know the length of one side, use this formula:
If you also know the apothem, you can use any of these three equivalent expressions:
All three expressions are equivalent and give the same result.
In a regular polygon like the decagon, the apothem is the shortest distance from the center to any side. The image below shows it clearly:
Click on any element to learn more.
