Maths-
General
Easy

Question

If for a matrix A, A3 = I then A–1 equals -

  1. A2    
  2. A    
  3. A3    
  4. None of these    

hintHint:

The inverse of matrix is another matrix, which on multiplication with the given matrix gives the multiplicative identity. For a matrix A, its inverse is A-1, and A · A-1 = A-1· A = I, where I is the identity matrix. The matrix whose determinant is non-zero and for which the inverse matrix can be calculated is called an invertible matrix.

The correct answer is: A2


     Given, A cubed equals I
    A cubed equals I

    Multiplying both sides by A to the power of negative 1 end exponent, we get
    rightwards double arrow A to the power of 3 space end exponent space A to the power of negative 1 end exponent equals I space A to the power of negative 1 end exponent

A to the power of 3 space end exponent space c a n space b e space s p l i t space i n t o space A squared space. space space A

rightwards double arrow A squared left parenthesis A space A to the power of negative 1 end exponent right parenthesis space equals space I space A to the power of negative 1 end exponent

W e space k n o w space t h a t space A A to the power of negative 1 end exponent space equals space I space a n d space I A to the power of negative 1 end exponent space equals space space A to the power of negative 1 end exponent space. space S u b s t i t u t i n g space t h e s e space v a l u e s space w e space g e t

rightwards double arrow A squared left parenthesis I right parenthesis equals space A to the power of negative 1 end exponent

rightwards double arrow A squared equals space A to the power of negative 1 end exponent

T h u s comma space i f space f o r space a space m a t r i x space A comma space A 3 space equals space I space t h e n space A – 1 space e q u a l s space minus space A squared

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