TITLE: How to calculate $\cos(6^\circ)$?
QUESTION [11 upvotes]: Do you know any method to calculate $\cos(6^\circ)$ ? 
I tried lots of trigonometric equations, but not found any suitable one for this problem.

REPLY [4 votes]: Here's one way to get a quick answer; use the taylor series. 6 degrees is 0.104719755 radians. Now the taylor series of cosine is $Cos(\theta)$=$\Sigma (-\theta) ^{2n}/2n!$. Putting the theta value of 0.104719755 gives you the approximation $Cos(6^{\circ})=0.99451688646$. Perfectly accurate up to 5 decimal places. In general, use the 17 degree rule. Sine and Cosine taylor approximations are good to the first order for about 17 degrees off of naught. You will have to excuse some of the odd language, I learned this first as a ship tech.