A line makes equal acute angles with the three coordinate axes. What is the cosine of each angle?

Explanation

1. 01

   With all three equal to $l$: $l^{2} + l^{2} + l^{2} = 1$.

2. 02

   $l^{2} = \frac{1}{3}$, and acute angles give $l = \frac{1}{\sqrt{3}}$.