Q31 / 75 · NTA Abhyas (JEE Main) 2020 · Mathematics · Matrices

Let α,β,γ be three real numbers satisfying α  β  γ  2-1  1-1-1-2-1  2  1=0  0  0. If the point Aα,β,γ lies on the plane 2x+y+3z=2, then 3α+2β-6γ is equal to

  • A
    0
  • Correct answer
    B
    -13
  • C
    1
  • D
    -3

Solution

α β γ2-11-1-1-2-121=0 0 0
2α-β-γ-α-β+2γα-2β+γ=0 0 0
⇒2α-β-γ=0
-α-β+2γ=0
α-2β+γ=0
Using cramer’s rule
∆=2-1-1-1-121-21=2-1+4+1-1-2-12+1
=6-3-3=0
So, the system of equations has infinite solutions
Put γ=k
2α-β=kα+β=2k⇒γ=k,β=k
⇒α,β,γ≡k,k,k
∵α,β,γ satisfies 2x+y+3z=2
⇒6k=2⇒k=13
α,β,γ≡13,13,13
⇒3α+2β-6γ=-13

Hence, the correct answer is option: 'B'.

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