Show that the vector $\hat i + \hat j + \hat k$ is equally inclined to the axes OX, OY and OZ.

Question

$\begin{array}{1 1}cos^{-1}\large\frac{1}{\sqrt3} \\cos^{-1}\large\frac{1}{3} \\ cos^{-1}\large\frac{1}{\sqrt2} \\cos^{-1}\large\frac{1}{2} \end{array}$