If `l_1, m_1, n_1` and `l_2,m_2, n_2` are direction cosines of the two lines inclined to each other at an angle `theta`, then the direction cosines of internal bisector of the angle between these lines are:
| A. |
`(l_1+l_2)/(2sin theta/2),(m_1+m_2)/(2sin theta/2), (n_1+n_2)/(2sin theta/2)` |
| B. |
`(l_1+l_2)/(2cos theta/2),(m_1+m_2)/(2cos theta/2), (n_1+n_2)/(2cos theta/2)` |
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| C. |
`(l_1-l_2)/(2sin theta/2),(m_1-m_2)/(2sin theta/2), (n_1-n_2)/(2sin theta/2)` |
| D. |
`(l_1-l_2)/(2cos theta/2),(m_1-m_2)/(2cos theta/2), (n_1-n_2)/(2cos theta/2)` |