Published by:
CGP EDU Academic Team
Published on: August 12, 2026
The straight lines whose direction cosines are given by 
are perpendicular, if
A
B
C
D
Text Solution
Verified by ExpertsThe correct answer is:
A
From the first relation, 
Put the value of n in second relation,
or 
.....(i)
Now if 
and 
be direction cosines of two lines, then from (i)
, 
or 
Similarly, elimination of l will yield 
(Say)
We know that the lines are perpendicular, if 
i.e., 
or 
.
Note: Student should remember this question as a fact.
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