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### Question Asked by a Student from EXXAMM.com Team

** Q 1845567463. ** If `l_1 , m_1 , n_1` aitd `l_2, m_2, n_2` are the direction cosines

of two mutually perpendicular lines, show that

the direction cosines of the line perpendicular

to both of these are `m_1 n_2 - m_2 n_1 , n_1 l_2 - n_2 l_1`,

`l_1 m_2 - l_2 m_1`