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

  • question_answer
    What is \[\frac{{{(1+i)}^{4n+5}}}{{{(1-i)}^{4n+3}}}\] equal to, where n is a natural number and \[i=\sqrt{-1}\]?

    A) 2                     

    B) \[2i\]  

    C) \[-2\]   

    D) i

    Correct Answer: A

    Solution :

    Given \[\frac{{{(1+i)}^{4n+5}}}{{{(1-i)}^{4n+3}}}\] \[=\frac{{{(1+i)}^{4n+3}}.{{(1+i)}^{2}}}{{{(1-i)}^{4n+3}}}={{\left( \frac{1+i}{1-i} \right)}^{4n+3}}.{{(1+i)}^{2}}\] \[={{\left[ \frac{(1+i)(1+i)}{(1-i)(1+i)} \right]}^{4n+3}}.(1+{{i}^{2}}+2i)\] \[={{\left[ \frac{1+{{i}^{2}}+2i}{1+1} \right]}^{4n+3}}.2i={{(i)}^{4n+3}}.2i=2{{(i)}^{4n+4}}\] \[=2.({{i}^{4(n+1)}})=2\]


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