@Resilient
I had one just like this and I found a way to get the correct solution with pencil but... your's is a bit to nasty to get a clean radian solution as skeeter says. you can check my thread how I did almost the same problem.
http://www.mathhelpforum.com/math-he...on-172605.html
I got yours into quadratic form in sin function but the coefficients have no common factors other then 1