The angle between the lines whose direction cosines satisfy the equations:
\[
l + m + n = 0 \quad \text{and} \quad m^2 + n^2 - l^2 = 0
\]
Find the angle between the two lines.
Show Hint
When dealing with direction cosines, use the relations between \( l \), \( m \), and \( n \) to simplify the problem, and apply the formula for the angle between two lines.