Class 12MathematicsTHREE DIMENSIONAL GEOMETRYSystem of co-ordinates, Direction cosines and direction ratios, Projection
EasyIf $\ell, m, n$ and $a, b, c$ are direction cosines of two lines, then:
- Athey are parallel when $\ell a + mb + nc = 0$
- Bthey are perpendicular when $\frac{\ell}{a} = \frac{m}{b} = \frac{n}{c}$
- Cthe direction ratios of the bisectors of the angles between the two lines are $\ell \pm a, m \pm b, n \pm c$
- Dthe direction ratios of the bisectors of the angles between the two lines are $\ell a, mb, nc$
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