How to calculate angle Given that radius is $7'$ and that tile width is $12''$, how many tiles are needed to close the full circle, when distance between each tile is $1/4''$, and at what angle does each tile need to be cut on both sides, so that when laid in a circle, sides of the tiles are parallel to each other. Can somebody point me in how to calculate this?
 A: This was probably not interesting question for you guys, but I think I have an idea how to calculate it.
Circumference of the circle is 43.98, let's round it up to 44. Since I want the tiles at the end not to be cut, and there will be overhand of 1", outer circle radius is 84 + 17 = 101. So outer circle circumference is 52.88', lets round it up to 53'. So basically inner circle is 9 feet shorter then outer one. Inner circle due to gap of 1/4" between tiles can hold only 43 tiles. So from these 43 tiles I have to take away 9'. 9x12 = 108/43 = 2.51. So from each tile I have to take away 2.5 inches, so on each side that is 1.25". Now if we apply trigonometry, since we know all the pieces we can calculate the angle of the cut. Based on opposite and adjacent side length, angle on the top of the tile is 3.97 degrees. I think that is pretty close to what others came up with. It is not absolutely necessary that it fits exactly as the circle will not be closed, only half circle will be created. 
