Question

If a variable line in two adjacent positions has direction cosines l, m, n and l + δl, m + δm, n + δn, show that the small angle δθ between the two positions is given by

δθ² = δl² + δm² + δn²

Answer 1

We have,  l, m, n and l + δl, m + δm, n + δn, as direction cosines of  a variable line of two different positions.