Comprehension

Direction: Consider the following for the items that follow:

Let L : x + y + z + 4 = 0 = 2x - y - z + 8 be a line and P : x + 2y + 3z + 1 = 0 be a plane. 

What are the direction ratios of the line?  

This question was previously asked in
NDA-II 2024 (Maths) Official Paper (Held On: 01 Sept, 2024)
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  1. 〈2, 1, -1〉
  2. 〈0, -1, 2〉
  3. 〈0, 1, -1〉
  4. 〈2, 3, -3〉

Answer (Detailed Solution Below)

Option 3 : 〈0, 1, -1〉
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Detailed Solution

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Explanation:

Given:

L = x + y + z + 4 = 0 = 2x – y – z + 8 and

P = x + 2y + 3z + 1 = 0 is a plane. 

⇒ Let direction ratios of line (a, b, c)

Since line is obtained by the intersection of planes.

⇒ x + y + z + 4 = 0 and 2x – y – z + 8 = 0

So a + b + c = 0....(i)

⇒ 2a – b – c = 0...(ii)

Solve (i) and (ii)

\(\frac{a}{-1+1} = \frac{b}{2+1} = \frac{c}{-1-2} =λ \)

⇒ a = 0, b = 3λ  and c = –3λ 

⇒ Direction ratios of line is (0, 3, –3) or (0, 1, –1).

∴ Option (c) is correct.

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