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JEE Main 20208 JanuaryMorning Shift
Exam
JEE Main
Year
2020
Date
8 January
Shift
Morning Shift
Subject
Mathematics
Chapter
Determinants

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

For which of the following ordered pairs (μ, ), the system of...

For which of the following ordered pairs (μ,δ),\left(\mu, \delta\right), the system of linear equations
x+2y+3z=1x + 2y + 3z = 1
3x+4y+5z=μ3x + 4y + 5z = \mu
4x+4y+4z=δ4x + 4y + 4z = \delta
is inconsistent?

Options

  1. A(4,3)\left(4, 3\right)
  2. B(4,6)\left(4, 6\right)
  3. C(1,0)\left(1, 0\right)
  4. D(3,4)\left(3, 4\right)

Correct answer

A. (4,3)\left(4, 3\right)

Step-by-step solution

D = \left|\begin{cases}3 & 4 & 5 \\ 1 & 2 & 3 \\ 4 & 4 & 4\end{cases}\right|\left({R}_{3} \to {R}_{3} - 2{R}_{1} + 3{R}_{2}\right)
= \left|\begin{cases}3 & 4 & 5 \\ 1 & 2 & 3 \\ 0 & 0 & 0\end{cases}\right| = 0
Now, let P3≡4x+4y+4z−δ=0.{P}_{3} ≡ 4x + 4y + 4z - \delta = 0 . If the system has solutions it will have infinite solution, so,P3≡αP1+βP2{P}_{3} ≡ \alpha{P}_{1} + \beta{P}_{2}
Hence, 3α+β=43\alpha + \beta = 4 and 4α+2β=4⇒α=2andβ=−24\alpha + 2\beta = 4 ⇒ \alpha = 2and\beta = - 2
So, for infinite solution 2μ−2=δ2\mu - 2 = \delta

For system to be inconsistent,

2μ≠δ+22\mu \ne \delta + 2
So, checking option, (4,3)( 4, 3 ) satisfies.

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