Q31 / 51 · JEE Advanced 2023 (Paper 1) · Mathematics

Let α, β and γ be real numbers. Consider the following system of linear equations

x+2y+z=7

x+αz=11

2x-3y+βz=γ

Match each entry in List-I to the correct entries in List-II.

  List-I   List-II
P If β=127α-3 and γ=28 then the system has 1  a unique solution
Q If β=127α-3 and γ≠28, then the system has 2 no solution
R If β≠127α-3 where α=1 and γ≠28, then the system has 3 infinitely many solutions
S If β≠127α-3 where α=1 and γ=28, then the system has 4 x=11, y=-2 and z=0 as a solution
    5 x=-15, y=4 and z=0 as a solution

The correct option is:

  • Correct answer
    A
    P→3, Q→2, R→1, S→4
  • B
    P→3, Q→2, R→5, S→4
  • C
    P→2, Q→1, R→4, S→5
  • D
    P→2, Q→1, R→1, S→3

Solution

Given,

System of equations,

x+2y+z=7

x+αz=11

2x-3y+βz=γ

Now finding Δ=12110α2-3β=0

⇒3α-2β-2α-3=0

⇒7α-2β=3

⇒β=127α-3

Now finding,

Δ3=12710112-3γ

Now equating, Δ3=0 we get,

⇒33-2γ-22+7-3=0

⇒γ=28

And Δ1=721110αγ-3β

 ⇒Δ1=21α-211β-αγ-33

⇒Δ1=21α-22β+2αγ-33

Similarly,  Δ2=171111α2γβ

⇒Δ2=11β-αγ-7β-2α+γ-22

⇒Δ2=14α+4β+γ-αγ-22

P If β=127α-3 and γ=28

Δ=0, Δ1=0, Δ2=0, Δ3=0

Infinitely many solutions

x=11, y=-2 and z=0 will satisfy all the three given equations, so it is a solution.

Q If β=127α-3 and γ≠28 then

Δ=0, but Δ3≠0 so no solution

R If β≠127α-3, α=1 and γ≠28

Δ≠0, Δ3≠0 so a unique solution

S If β≠127α-3, α=1, γ=28

Δ≠0, Δ3=0, Δ1≠0, Δ2≠0, so a unique solution

x=11, y=-2 and z=0 will satisfy all the three equations

Option A is correct.  

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

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