The acute angle between two lines such that the direction

Question:

The acute angle between two lines such that the direction cosines $\ell, \mathrm{m}, \mathrm{n}$ of each of them satisfy the equations $\ell+\mathrm{m}+\mathrm{n}=0$ and $\ell^{2}+\mathrm{m}^{2}-\mathrm{n}^{2}=0$ is :-

  1. $30^{\circ}$

  2. $45^{\circ}$

  3. $60^{\circ}$

  4. $15^{\circ}$


Correct Option: 3,

Solution:

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