Hi,

I must show that $\displaystyle (\forall k \in \mathbb{Z}) \forall x \in ]-\frac{\pi}{2}+k\pi;\frac{\pi}{2}+k\pi[: Arctan(tanx)=x-k\pi.$

I know just that $\displaystyle Arctan(tanx)=x$ when $\displaystyle x \in ]-\frac{\pi}{2}+k\pi;\frac{\pi}{2}+k\pi[$

Can you help me???