JEE Main & Advanced Mathematics Complex Numbers and Quadratic Equations Question Bank Self Evaluation Test - Complex Numbers and Quadratic Equations

  • question_answer
    What is the value of \[{{\left( -\sqrt{-1} \right)}^{4n+3}}+{{\left( {{i}^{41}}+{{i}^{-257}} \right)}^{9}},\] where \[n\in N\]?

    A) 0         

    B) 1    

    C) i                      

    D) \[-i\]

    Correct Answer: C

    Solution :

    Consider \[{{(-\sqrt{-1})}^{4n+3}}\,+{{({{i}^{41}}-{{i}^{-257}})}^{9}}\] \[=\,{{(-i)}^{4n+3}}+{{\left[ {{({{i}^{4}})}^{10}}.\,{{i}^{1}}+{{({{i}^{3}})}^{-85}}.\,{{i}^{-\,2}} \right]}^{9}}\] \[=\,\,{{(-i)}^{4n+3}}+{{\left[ i+\frac{1}{{{({{i}^{3}})}^{85}}}.\frac{1}{{{i}^{2}}} \right]}^{9}}\] \[=\,\,{{(-i)}^{4n+3}}+{{\left( i+\frac{1}{i} \right)}^{9}}\] \[=\,\,-{{(-1)}^{4n+3}}\,{{(i)}^{4n}}\,{{(i)}^{3}}\,+{{(i\,-\,\,i)}^{9}}=\,\,-(1)\,(-i)+0\,\,=\,\,i\]


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