Composite siding wall

How do I cut boards for a 20 sided deck?

I am in the process of building a deck around my 15 foot pool and would like to use a 20 sided polygon for this to ensure that I can get as close to the shape of the pool as possible as to support the sides of the pool. I would like to know if you could help me with two things. The first being the angle to cut the boards using the miter saw and the second being the length of each of the 20 boards thatI am using (2x4). My husband and I are doing this project together and don't know a whole lot about carpentry but we will try any project once.

The angle. If it were a four sided deck, each corner would have to be 90, so each board would be cut at 45 (90 divided by 2). Therefore, each corner in a 20 sided deck would be 360 divided by 20 equals 18. Therefore each board should be cut at 9. The length. The pool has a diameter of 15 ft. Therefore it has a circumference of Pi times the diameter, or 47.143 feet. Therefore, if the boards were slightly curved, the short side of the boards (closest to the pool) would be 47.143 divided by 20 equals 2.357 ft. long. The boards will have to be slightly longer, because they are not curved. Therefore, the inside length of the boards will likely be in the vicinity of 2' 5" or 2' 6". This will depend on the exact diameter of the pool. Remember, that the outside length of the board will be greater because you are cutting them on angle. Each successive board, as you get further and further from the pool, will have to be longer. We might suggest you consider a 16 sided deck, to make the mathematics a little easier. Start with a four sided deck on paper. Now convert it to an 8 sided deck on paper, and divide again to create 16 sides.