Need help solving , i have tried to do the following:
after this i contiue and i couldn't find the solution.
There is something wrong with your first equation. You cannot divide an equation. You need to put the fraction on both sides :
This simplifies trivially to :
Now you can use the trigonometric identity :
Use this again :
And you are left with a quadratic equation, which can be easily solved for , and thus for .
You got it wrong between the third and the fourth line :