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Question: Answered & Verified by Expert
If the lines x-12=y-1=z2 and x-y+z-2=0=λx+3z+5 are coplanar, then the value of 7λ is equal to
MathematicsThree Dimensional GeometryJEE Main
Options:
  • A 31
  • B -52
  • C -39
  • D -31
Solution:
2521 Upvotes Verified Answer
The correct answer is: -31

A plane passing through the line of intersection of the given 2 planes is x-y+z-2+μλx+3z+5=0
x1+λμ-y+z1+3μ+5μ-2=0
Since the given line x-12=y-1=z2 must lie in this plane
21+λμ+-1-1+1+3μ2=0
2+2λμ+1+2+6μ=0
2λμ+6μ+5=0..i
The point 1,0,0 must satisfy the equation of the plane
1+λμ-0+0+5μ-2=0
λμ+5μ-1=0ii
Solving i and ii we get,

μ=74, λ=-317

7λ=-31

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