If l_1, m_1 , n_1 , l_2 , m_2, n_2 and l_3 , m_3 , n_3 are the direction cosines of three mutually perpendicular lin

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Q 1860634515.     If l_1, m_1 , n_1 , l_2 , m_2, n_2 and l_3 , m_3 , n_3 are the direction cosines of three mutually perpendicular lines, then prove that the line whose direction cosines are proportional to l_1 + l_2 + l_3 , m_1 + m_2 + m_3 and n_1 + n_2 + n_3 makes equal angles with them .

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