Trigonometric equations

• May 14th 2006, 04:33 PM
LilDragonfly
Trigonometric equations
Find the general solutions of:
cos 50 + cos 30 = 0
• May 14th 2006, 06:52 PM
ThePerfectHacker
Quote:

Originally Posted by LilDragonfly
Find the general solutions of:
cos 50 + cos 30 = 0

I presume you know that given,
$\cos x=a$ you know what to find all the solutions.
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Use cosine angle sum identity on,
$\cos 5x+\cos 3x=0$
To get,
$2\cos 4x\cos x=0$
Thus, each factor is zero,
$\cos 4x=0$
$\cos x=0$