While reading the general solutions of trigonometric equations, I came to this:
The equation $\sin\theta = k$ is satisfied by two values of $\theta$ of the form $\alpha$ & $\pi - \alpha$ in the interval $0 \leq \theta \leq 2\pi$ .
Ok. But when I read the result for $\cos\theta = k$, the interval was given $-\pi < \theta \leq \pi$ .
Now, I want to know what is the cause for the different intervals. Can't they be same? I want to post this but not getting any proper title. Can anyone please suggest me a good title which portrays my problem?