Why $\cos(-\theta)$ gives positive values while in case of sine it is negative? Why $\cos(-\theta)$ gives positive values while in case of sine it is negative?
I mean
$\cos(-\theta) = +\cos(\theta)$
$\sin(-\theta) = -\sin(\theta)$
$\tan(-\theta) = -\tan(\theta)$
and please explain General Angles in simple worlds?

The series expansipns of cos and sin are:
$cos (x)= \sum_{n=0}^\infty\frac {(-1)^nx^{2n}}{(2n)!}=1-x^2/2+x^4/4!\pm...$ and
$sin (x)= \sum_{n=0}^\infty\frac {(-1)^nx^{2n+1}}{(2n+1)!}=x-x^3/3!+x^5/5!\pm...$
Notoce here that changing the sign for cos makes no difference, (as we have all even powers of x)  but changing the sign for sin does (since we have all odd powers of x).
Also $\tan (-\theta)=\frac {sin (-\theta)}{cos (-\theta)}\frac {-sin (\theta)}{cos (\theta)}=-tan (\theta)$.
