The direction cosines of a line which makes equal angles with the co-ordinate axes are____

The direction cosines of a line which makes equal angles with the co-ordinate axes are____
  1. -13,13,13
  2. 13,13,13
  3. ±13,±13,±13
  4. 1213,513,0

Solution

Let l, m, n = cos α, cos β, cosγ

are direction cosines.

We know that l, m, n are direction cosines then l2+m2+n2=1

Given that they are making equal angles with axes

i.e cos α = cos β = cos γ

3cos2 α = 1

cos α = ±13

So Required is ±13, ±13, ±13.

Asked in: AP EAMCET 2021 (19 Aug Shift 1)

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