JEE Main & Advanced Mathematics Determinants & Matrices Question Bank Self Evaluation Test - Matrices

  • question_answer
    Elements of a matrix A of order \[10\times 10\] are defined as \[{{a}_{ij}}={{w}^{i+j}}\] (where w is cube root of unity), then trof the matrix is

    A) 0

    B) 1

    C) 3

    D) None of these

    Correct Answer: D

    Solution :

    [d] \[tr(A)=\sum\limits_{i=j}{{{a}_{ij}}}=({{a}_{11}}+{{a}_{22}}+{{a}_{33}}+....+{{a}_{10}})\] \[=({{w}^{2}}+{{w}^{4}}+{{w}^{6}}+....+{{w}^{20}})=\]                         \[{{w}^{2}}(1+{{w}^{2}}+{{w}^{4}}+...+{{w}^{18}})\] \[={{w}^{2}}[(1+w+{{w}^{2}})+...+(1+w+{{w}^{2}})+1]\]                         \[={{w}^{2}}\times 1={{w}^{2}}\]


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