3 and 4 .Determinants and Matrices
easy

The matrix $A = \left[ {\begin{array}{*{20}{c}}{1/\sqrt 2 }&{1/\sqrt 2 }\\{ - 1/\sqrt 2 }&{ - 1/\sqrt 2 }\end{array}} \right]$ is

A

Unitary

B

Orthogonal

C

Nilpotent

D

Involutory

Solution

(c) ${A^2} = A\,.\,A = \left[ {\begin{array}{*{20}{c}}{1/\sqrt 2 }&{1/\sqrt 2 }\\{ – 1/\sqrt 2 }&{ – 1/\sqrt 2 }\end{array}} \right]\,\left[ {\begin{array}{*{20}{c}}{1/\sqrt 2 }&{1/\sqrt 2 }\\{ – 1/\sqrt 2 }&{ – 1/\sqrt 2 }\end{array}} \right]$

$ = \left[ {\begin{array}{*{20}{c}}0&0\\0&0\end{array}} \right] = O$

$\therefore $ Matrix $A$ is nilpotent of order  $2$ .

Standard 12
Mathematics

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