Maths challenge (I'm going to do it too):
h²sin²(s/2r) = h² - 2hd + d² + 2hr - 2rd +r² -2rhcos(s/2r) + 2drcos(s/2r) - 2r²cos(s/2r) + r²cos²(s/2r)
Solve for d.
In this equation, I am modeling the declination by using three collinear flag poles, at a height h above still water. A laser is used to point from the top of the first pole to the top of the last. d is the distance between the top of the middle pole and the point where the laser light points. r is the radius of the earth, s is the co-ordinate distance. You can get this by drawing it how I explained it hopefully, as well everyone makes mistakes, especially during a lot of derivation lol. Again, sin and cos need radians here, as i cannot be bothered with stupid factors of 180/pi tbh.
The equation can be brute-forced by completing the square/quadratic formula, however elegance is always good in proofs. Since there appears to be two roots due to the quadratic nature of the problem, any solutions below zero or above h are unphysical. If anyone finds two roots between zero and h, tell me because I have made a mistake.