Find the angle between the lines whose direction cosines are given by the equations: 3l + m + 5n = 0 and 6mn – 2nl + 5lm = 0.
Eliminating m from the given two equations, we get
Thus the direction ratios of two lines are proportional to – n, –2n, n and –2n, n, n,
i.e. 1, 2, –1 and –2, 1, 1.
So, vectors parallel to these lines are
