Compute the value of .
Solution
Consider a 360-sided regular polygon with side length 1, rotated so that its sides are at half-degree inclinations (that is, its sides all have inclinations of , and so on. Go to the bottom point on this polygon and then move clockwise, numbering the sides as you go. Then, take the section of 15 sides from side 31 to side 45. These sides have inclinations of , and so on, up to . Therefore, over this section, the horizontal and vertical displacements are, respectively: . However, we can also see that, letting be the circumradius of this polygon: . From these, we can easily compute that our desired answer is .
Want a route through all this instead of an archive? The track
puts 2,000 problems in a working order, from AMC 10 level to the IMO shortlist.