Q48 / 90 · JEE Main 2024 (30 Jan Shift 2) · Mathematics

Consider the system of linear equations x+y+z=5,x+2y+λ2z=9 and x+3y+λz=μ, where λ,μ∈R. Then, which of the following statement is NOT correct ?

  • A
    System has infinite number of solution if λ=1 and μ=13
  • B
    System is inconsistent if λ=1 and μ≠13
  • Correct answer
    C
    System has unique solution if λ≠1 and μ≠13
  • D
    System is consistent if λ≠1 and μ=13

Solution

Given: 

x+y+z=5

x+2y+λ2z=9

 x+3y+λz=μ

⇒△=11112λ213λ

⇒△=2λ-3λ2-λ+λ2+1

⇒△=-2λ2+λ+1

We know that for infinite solutions, △=0 & △1=△2=△3=0 

⇒-2λ2+λ+1=0

⇒2λ2-λ-1=0

⇒λ-12λ+1=0

⇒λ=1, -12

Now, finding △1 for λ=1 we get,

Δ1=511921μ31

⇒Δ1=μ-13

And for λ=-12 we get,

Δ1=5119214μ3-12=14514921μ3-2=7413-μ

So, for λ≠1 & μ≠13 system has no solution,

Hence, option C is the correct answer.

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

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