Question

Show that the three lines with direction cosines

12/13,-3/13,-4/13,4/13,12/13,3/13,3/13,-4/13,12/13 are mutually perpendicular.

Answer 1

Two lines with direction cosines, l_1, m₁, n₁ and l₂, m_2, n_2, are perpendicular to each other, if l₁l₂ + m₁m₂ + n₁n₂ = 0

Therefore, the lines are perpendicular. 

Thus, all the lines are mutually perpendicular.