Hey guys this question is gonna sound pretty dumb, but I never learned how to do this. What if I want to find say, cos(pi/5) but I don't have a calculator? Even if I did have a calculator, I want it in nice values, like square roots, rather than decimals anyway. If I have something like cos(pi/8) I think I know how to find something like that using double angle formula cos(2x)=2cos2x-1, because I know the value of cos(4pi) and cos(2pi), but when I have an odd value I'm stuck at what to do. Is there any simple algorithmic process I can use? Someone mentioned to me about finding complex roots, but I'm not sure how that works?