1. ## cos2pi

why is cos2pi = +- 1? its not logical, since cosA = sinA/tanA and sin A = tan A = 0....
??

2. Originally Posted by furor celtica
why is cos2pi = +- 1? its not logical, since cosA = sinA/tanA and sin A = tan A = 0....
??
$2\pi$ radians is a full revolution of the unit circle. So you end up back exactly where you started at an angle of 0, and so the horizontal distance (the cosine) will be exactly the same.

What's $\cos{0}$ equal?

BTW you can't work out $\cos{2\pi} = \frac{\sin{2\pi}}{\tan{2\pi}}$ because the function $\tan{x}$ is defined by $\frac{\sin{x}}{\cos{x}}$.

It would be the same as saying you're trying to find $x$ if $x = x$...