AP EAMCET · Maths · Three Dimensional Geometry
Which of the following is false?
1. If \((a, b, c)\) are direction ratios of a line, then \(a^2+b^2+c^2 \neq 1\).
2. The direction cosines of a line can be its direction ratios but not vice-versa.
3. If \((l, m, n)\) is one set of direction cosines, then \((-l,-m,-n)\) is also a valid set.
4. If \(\left(l_1, m_1, n_1\right)\) and \(\left(l_2, m_2, n_2\right)\) are direction cosines of perpendicular lines, then \(l_1 l_2+m_1 m_2+n_1 n_2=1\).
- A 1
- B 2
- C 3
- D 4
Answer & Solution
Correct Answer
(D) 4
Step-by-step Solution
Detailed explanation
If the direction cosines of two perpendicular lines are \(l_1, m_1, n_1\) and \(l_2, m_2, n_2\), then \(l_1 l_2+m_1 m_2+n_1 n_2=0\)
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