# Thread: Trig: Compound Angle Formulas

1. ## Trig: Compound Angle Formulas

Can someone explain to me how you would solve this question:

cos23(pi)
-------
12

2. Originally Posted by skeske1234
Can someone explain to me how you would solve this question:

cos2(pi)
-------
12

Hi

Do you mean $\cos \frac{2\pi}{12}$ or $\frac{\cos 2\pi}{12}$ or anything else ?

3. Originally Posted by running-gag
Hi

Do you mean $\cos \frac{23\pi}{12}$ or $\frac{\cos 23\pi}{12}$ or anything else ?
I mean:

$\cos \frac{23\pi}{12}$

$\cos \frac{23\pi}{12}$
$\cos \frac{23\pi}{12} = \cos \left(-\frac{\pi}{12}\right) = \cos \frac{\pi}{12}$
Then using $\cos 2a = 2 \cos^2 a - 1$ and $\cos \frac{\pi}{6} = \frac{\sqrt{3}}{2}$ you can compute $\cos \frac{\pi}{12}$