Find the general solutions of:
cos 50 + cos 30 = 0
I presume you know that given,Originally Posted by LilDragonfly
$\displaystyle \cos x=a$ you know what to find all the solutions.
---------
Use cosine angle sum identity on,
$\displaystyle \cos 5x+\cos 3x=0$
To get,
$\displaystyle 2\cos 4x\cos x=0$
Thus, each factor is zero,
$\displaystyle \cos 4x=0$
$\displaystyle \cos x=0$