Class 12MathematicsTHREE DIMENSIONAL GEOMETRYSystem of co-ordinates, Direction cosines and direction ratios, Projection
MediumIf two lines are parallel to each other,then which of the following is true? (If $(l_1, m_1, n_1)$ and $(l_2, m_2, n_2)$ are direction cosines of the two lines).
- A$l_1 l_2 + m_1 m_2 + n_1 n_2 = 0$
- B$\Sigma(l_1 l_2 - m_2 m_1)^2 = 0$
- C$\frac{l_1}{l_2} = \frac{m_1}{m_2} = \frac{n_1}{n_2}$
- D$l_1 l_2 + m_1 m_2 + n_1 n_2 = 1$
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