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JEE Main 20208 JanuaryEvening Shift
Exam
JEE Main
Year
2020
Date
8 January
Shift
Evening Shift
Subject
Mathematics
Chapter
Determinants

JEE Main 2020 · 8 January · Evening Shift · Mathematics · Determinants

The system of linear equations + 2y + 2z = 5 2 + 3y + 5z = 8 4x + +...

The system of linear equations
\lambdax+2y+2z=5\lambdax + 2y + 2z = 5
2\lambdax+3y+5z=82\lambdax + 3y + 5z = 8
4x+\lambday+6z=104x + \lambday + 6z = 10 has

Options

  1. Ano solution when λ=8\lambda = 8
  2. Ba unique solution when λ=−8\lambda = - 8
  3. Cno solution when λ=2\lambda = 2
  4. Dinfinitely many solutions when λ=2\lambda = 2

Correct answer

C. no solution when λ=2\lambda = 2

Step-by-step solution

∆ = \left|\begin{cases}\lambda & 2 & 2 \\ 2\lambda & 3 & 5 \\ 4 & \lambda & 6\end{cases}\right| = \lambda\left(18 - 5\lambda\right) - 2\left(12\lambda - 20\right) + 2\left(2{\lambda}^{2} - 12\right) = - {\lambda}^{2} - 6\lambda + 16 = \left(\lambda + 8\right)\left(2 - \lambda\right)
∆=0∆ = 0 for λ=2\lambda = 2,
{∆}_{1} = \left|\begin{cases}5 & 2 & 2 \\ 8 & 3 & 5 \\ 10 & 2 & 6\end{cases}\right|

∆1=5[18−10]−2[48−50]+2[16−30]{∆}_{1} = 5\left[18 - 10\right] - 2\left[48 - 50\right] + 2\left[16 - 30\right]

∆1=40+4−28≠0{∆}_{1} = 40 + 4 - 28 \ne 0
No solution for λ=2\lambda = 2.

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