Khẳng định nào sau đây là đúng A. cos u

$\cos u = \cos v \Leftrightarrow \left[ \begin{gathered}

u = v + k2\pi \hfill \\

u = \pi - v + k2\pi \hfill \\

\end{gathered} \right.\left( {k \in \mathbb{Z}} \right)$.

$\cos u = \cos v \Leftrightarrow \left[ \begin{gathered}

u = v + k2\pi \hfill \\

u = - v + k2\pi \hfill \\

\end{gathered} \right.\left( {k \in \mathbb{Z}} \right)$.

$\cos u = \cos v \Leftrightarrow \left[ \begin{gathered}

u = v + k\pi \hfill \\

u = \pi - v + k\pi \hfill \\

\end{gathered} \right.\left( {k \in \mathbb{Z}} \right)$.

$\cos u = \cos v \Leftrightarrow \left[ \begin{gathered}

u = v + k\pi \hfill \\

u = - v + k\pi \hfill \\

\end{gathered} \right.\left( {k \in \mathbb{Z}} \right)$.