Find the area of a regular decagon with perimeter 100 units. show all work.

A regular polygon has ten (10) equal sides ( since it is regular).
We are given with the perimeter value which is 100 units and the perimeter formula is P = 10a
Solving for a (the side measurement), we have:
100 = 10a
a= 100/10
a =10

We can now proceed in solving the area and the formula is shown below:
Area = 5/2 a√ (5+2√5)
Area = 5/2 * 10√(5+2√5)
Area = 76.94 square units

The answer is 96.94 square units.