Fun with maths: prove Cos pi/7 + cos 3pi/7 + cos 5pi/7=1/2
To prove Cos pi/7 + cos 3pi/7 + cos 5pi/7=1/2 let z = cos pi/7 + i sin pi/7 z^7 = cos pi + i sin pi = - 1 so z^7+1 = 0 (z+1) (z^6-z^5+z^4 - z^3+z^2 -z + 1) = 0 as z is not - 1 so z^6-z^5+z^4 - z^3+z^2 -z + 1 = 0 so z^6-z^5+z^4 - z^3+z^2 -z= -1 so z+z^3+ z...