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NDA 2024
Exam
NDA
Year
2024
Subject
Mathematics
Chapter
Three Dimensional Geometry

NDA 2024 · Mathematics · Three Dimensional Geometry

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

Paragraph: Let L:x+y+z+4=0=2x−y−z+8\mathrm{L}: x+y+z+4=0=2 x-y-z+8 be a line and P : x+2y+3z+1=0x+2 y+3 z+1=0 be a plane
Question: What are the direction ratios of the line?

Options

  1. A<2,1,−1>< 2,1,-1 >
  2. B<0,−1,2>< 0,-1,2 >
  3. C<0,1,−1>< 0,1,-1 >
  4. D<2,3,−3>< 2,3,-3 >

Correct answer

C. <0,1,−1>< 0,1,-1 >

Step-by-step solution

We have L:x+y+z+4=0=2x−y−z−8\mathrm{L}: \mathrm{x}+\mathrm{y}+\mathrm{z}+4=0=2 \mathrm{x}-\mathrm{y}-\mathrm{z}-8 and P: x+2 y+3 z+1=0 is a plane. Let Dr's of line ⟨\langle a, b, c ⟩\rangle Since, line LL obtained by intersection of planes x+y+z+4=0 and 2x−y−z−8=0x+y+z+4=0 \text{ and } 2 x-y-z-8=0 So, a+b+c=0\mathrm{a}+\mathrm{b}+\mathrm{c}=0 .....(i) 2a−b−c=02 a-b-c=0 ....(ii) (line is perpendicular to normal of both plane) a−1+1=b2+1=c−1−2=λ⇒a=0,b=3λ,c=−3λ\begin{aligned} & \frac{\mathrm{a}}{-1+1}=\frac{\mathrm{b}}{2+1}=\frac{\mathrm{c}}{-1-2}=\lambda \\ & \Rightarrow \mathrm{a}=0, \mathrm{ b}=3 \lambda, \mathrm{c}=-3 \lambda \end{aligned} (solving (i) and (ii) Dr's of line is ⟨0,3,−3⟩or⟨0,1,−1⟩\langle 0,3,-3\rangle or \langle 0,1,-1\rangle
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