MCQ
If a matrix  $A$  is such that $3{A^3} + 2{A^2} + 5A + I = 0,$ then its inverse is
  • $ - (3{A^2} + 2A + 5I)$
  • B
    $3{A^2} + 2A + 5I$
  • C
    $3{A^2} - 2A - 5I$
  • D
    None of these

Answer

Correct option: A.
$ - (3{A^2} + 2A + 5I)$
a
(a) $3{A^3} + 2{A^2} + 5A + I = 0 $

$\Rightarrow I = - 3{A^3} - 2{A^2} - 5A$

$ \Rightarrow $$I{A^{ - 1}} = - 3{A^2} - 2A - 5I$

$ \Rightarrow $ ${A^{ - 1}} = - (3{A^2} + 2A + 5I)$

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