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If the lines andx-1-3=y-22k=z-32andx-13k=y-11=z-6-5 are perpendicular, find the value of k.

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Question

If the lines `(x-1)/(-3) = (y -2)/(2k) = (z-3)/2 and (x-1)/(3k) = (y-1)/1 = (z -6)/(-5)` are perpendicular, find the value of k.

Sum
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Solution 1

The direction ratios of the given lines are – 3, 2k, 2 and 3k, 1, −5.

∵ If the lines are perpendicular then a1a2 + b1b2 + c1c2 = 0

∴ – 3.3k + 2k.1 + 2.( –5) = 0

⇒ 9k + 2k – 10 = 0

⇒ −7k = 10

k = `(-10)/7`

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Solution 2

The given lines are,

`(x - 1)/-3 = (y - 2)/(2k) = (z - 3)/2`                 ....(i)

and `(x - 1)/(3k) = (y - 1)/1 = (z - 6)/-5`          ....(ii)

The direction ratio of the line (i) are < - 3, 2k, 2 >

The direction ratio of the line (ii) are < 3k, 1, -5 >

if -9k + 2k - 10 = 0 if 7k = -10 if `k = -10/7`

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Chapter 11: Three Dimensional Geometry - Exercise 11.4 [Page 498]

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NCERT Mathematics Part 1 and 2 [English] Class 12
Chapter 11 Three Dimensional Geometry
Exercise 11.4 | Q 6 | Page 498

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