If $A=\left(\begin{array}{c}\alpha-1 \\ 0 \\ 0\end{array}\right), B=\left(\begin{array}{c}\alpha+1 \\ 0 \\…

If $A=\left(\begin{array}{c}\alpha-1 \\ 0 \\ 0\end{array}\right), B=\left(\begin{array}{c}\alpha+1 \\ 0 \\ 0\end{array}\right)$ be two matrices, then $A B^T$ is a non-zero matrix for $|\alpha|$ not equal to
  1. 2
  2. 0
  3. 1
  4. 3

Solution

Let $A=\left(\begin{array}{c}\alpha-1 \\ 0 \\ 0\end{array}\right), B=\left(\begin{array}{c}\alpha+1 \\ 0 \\ 0\end{array}\right)$ be two matrices. $ \begin{aligned} & A B^T=\left(\begin{array}{c} \alpha-1 \\ 0 \\ 0 \end{array}\right)(\alpha+1 \quad 0 \quad 0) \\ & =\left(\begin{array}{ccc} \alpha^2-1 & 0 & 0 \\ 0 & 0 & 0 \\ 0 & 0 & 0 \end{array}\right) \\ & \end{aligned} $

Asked in: JEE Main 2012 (07 May Online)

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