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Let A be a `nxxn` matrix such that`A ^(n) = alpha A,` where `alpha ` is a real number different from 1 and - 1. The matrix `A + I_(n)` isA. singularB. invertibleC. scalar matrixD. None of these |
Answer» Correct Answer - B Let `B=A + I_(n)` `therefore A= B-I_(n)` Given, `A^(n) =alpha A ` `rArr (B-I_(n) ) ^(n) = alpha (B-I_(n))` `rArr B^(n) -""^(n)C_(1) B^(n-1) + ""^(n) C_(2) B^(n-2) +...+ (-1) ^(n) I_(n)` `= alpha B - alphaI_(n)` `rArr B( B^(n-1) -""^(n)C_(1) B^(n-2) + ""^(n) C_(2) B^(n-3) +...+ (-1) ^(n-1) I_(n)-alphaI_(n))` `= [(-1)^(n+1) - alpha ]I_(n ) ne 0 [ because alpha ne pm 1]` Hence, B is invertible. |
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