## Elementary Geometry for College Students (5th Edition)

$35^{\circ}$
The length of the diagonal of the base of a cube is equal to $\sqrt2 s$. Thus, we find: $tan(\alpha) = \frac{s}{\sqrt{2}s} \\ \alpha = \tan^{-1}( \frac{1}{\sqrt2}) = 35^{\circ}$