The number of $3 \times 3$ matrices $A$ whose entries are either 0 or 1 and for which the system…

The number of $3 \times 3$ matrices $A$ whose entries are either 0 or 1 and for which the system $A\left[\begin{array}{l}x \\ y \\ z\end{array}\right]=\left[\begin{array}{l}1 \\ 0 \\ 0\end{array}\right]$ has exactly two distinct solutions, is
  1. 0
  2. $2^9-1$
  3. 168
  4. 2

Solution

Since, $A\left[\begin{array}{l}x \\ y \\ z\end{array}\right]=\left[\begin{array}{l}1 \\ 0 \\ 0\end{array}\right]$ is linear equation in three variables and that could have only unique, no solution or infinitely many solution. $\therefore$ It is not possible to have two solutions. Hence, number of matrices $A$ is zero.

Asked in: JEE Advanced 2010 (Paper 1)

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