If the direction cosines of a variable line in two adjacent points be `l, M, n and l+deltal,m+deltam+n+deltan` the small angle `deltatheta`as between the two positions is given by

Explanation

To find the small angle \( \delta \theta \) between two positions of a variable line with direction cosines \( l, m, n \) and \( l + \delta l, m + \delta m, n + \delta n \), we can follow these steps:

### Step 1: Understand the Properties of Direction Cosines
The direction cosines of a line are defined such that:
\[ l^2 + m^2 + n^2 = 1 \]
This equation holds for any direction cosines.
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