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JEE Mains · Maths · STD 12 - 3 and 4 . metrices and determinant

Let \(S_1\) and \(S_2\) be respectively the sets of all \(a \in R -\{0\}\) for which the system of linear equations \(a x+2 a y-3 a z=1\) \((2 a+1) x+(2 a+3) y+(a+1) z=2\) \((3 a+5) x+(a+5) y+(a+2) z=3\) has unique solution and infinitely many solutions. Then

  1. A \(n \left( S _1\right)=2\) and \(S _2\) is an infinite set
  2. B \(S_1\) is an infinite set an \(n\left(S_2\right)=2\)
  3. C \(S _1=\Phi\) and \(S _2= R -\{0\}\)
  4. D \(S _1= R -\{0\}\) and \(S _2=\Phi\)
Verified Solution

Answer & Solution

Correct Answer

(D) \(S _1= R -\{0\}\) and \(S _2=\Phi\)

Step-by-step Solution

Detailed explanation

\begin{array}{l}\Delta=\left|\begin{array}{lll}a & 2 a & -3 a \\ 2 a+1 & 2 a+3 & a+1 \\ 3 a+5 & a+5 & a+2\end{array}\right| \\ =a\left(15 a^2+31 a+36\right)=0 \Rightarrow a=0 \\ \Delta \neq 0 \text { for all } a \in R-\{0\} \\ \text { Hence } S_1=R-\{0\} \quad S_2=\Phi\end{array}

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