Three Dimensional Geometry
NCERT Exemplar Class 12
CBSE
Grade 12
Question:
If lines $\dfrac{x-1}{-3} = \dfrac{y-2}{2k} = \dfrac{z-3}{2}$ and $\dfrac{x-1}{3k} = \dfrac{y-1}{1} = \dfrac{z-6}{-5}$ are perpendicular, $k$ is:
(a) $-10/7$
(b) $10/7$
(c) $-7/10$
(d) $7/10$
Step-by-Step Solution
a1 a2 + b1 b2 + c1 c2 = -9k + 2k - 10 = 0 => -7k = 10 => k = -10/7. [1.0 Mark]
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🎯 Official CBSE Marking Scheme:
Selecting $-10/7$: 1.0 Mark
Correct Answer: $-10/7$
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