The direction angles of vector \((a,b,c)\) are \(\alpha\), \(\beta\), and \(\gamma\), which are the angles the vector makes with the positive \(x\), \(y\), and \(z\) axes, respectively.
These angles are restricted to be
\[0^\circ \leq \alpha, \beta, \gamma \leq 180^\circ\]
For example, in the diagram
\[\cos(\gamma) =\dfrac{c}{\lvert \overrightarrow{OP}\rvert}\]
Similarly,
\[\cos(\alpha)=\dfrac{a}{\lvert \overrightarrow{OP} \rvert} \qquad \cos(\beta)=\dfrac{b}{\lvert\overrightarrow{OP}\rvert}\]