JEE Main & Advanced Mathematics Complex Numbers and Quadratic Equations Question Bank Square root, Representation and Logarithm of complex numbers

  • question_answer
    If \[\sqrt{x+iy}=\pm (a+ib),\] then \[\sqrt{-x-iy}\] is equal to

    A) \[\pm (b+ia)\]

    B) \[\pm (a-ib)\]

    C) \[\pm (b-ia)\]

    D) None of these

    Correct Answer: C

    Solution :

    \[\sqrt{x+iy}=\pm (a+bi)\] Þ  \[x+iy={{a}^{2}}-{{b}^{2}}+2iab\] Þ \[x={{a}^{2}}-{{b}^{2}},\]\[y=2ab\] \ \[\sqrt{-x-iy}=\sqrt{-({{a}^{2}}-{{b}^{2}})-2iab}=\sqrt{{{b}^{2}}-{{a}^{2}}-2iab}\]                      \[=\sqrt{{{(b-ia)}^{2}}}=\pm (b-ia)\].


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