Q42 / 68 · NEST (NISER) 2023 (Session 1) · Mathematics

Let $\alpha$ be a complex number such that $\alpha \neq 1$ and $\alpha^5=1$. Let $A=\left(\begin{array}{lll}0 & 0 & \alpha \\ 0 & \alpha & 0 \\ \alpha & 0 & 0\end{array}\right)$ and $I$ denote the identity matrix. Then the value of $I+A+A^2+A^3+A^4$ is

  • Correct answer
    A
    $\left(1+\alpha^2+\alpha^4\right)\left(\begin{array}{ccc}1 & 0 & -1 \\ 0 & 0 & 0 \\ -1 & 0 & 1\end{array}\right)$
  • B
    $\alpha\left(1+\alpha^2\right)\left(\begin{array}{ccc}1 & 0 & -1 \\ 0 & 0 & 0 \\ -1 & 0 & 1\end{array}\right)$
  • C
    $\left(1+\alpha^2+\alpha^4\right)\left(\begin{array}{ccc}-1 & 0 & 1 \\ 0 & 0 & 0 \\ 1 & 0 & -1\end{array}\right)$
  • D
    $\left(1+\alpha^2+\alpha^4\right)\left(\begin{array}{ccc}-1 & 0 & 1 \\ 0 & 1 & 0 \\ 1 & 0 & -1\end{array}\right)$

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

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