CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2008

  • 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)  \[(ai+b)\]         

    D)         \[\pm (b-ia)\]

    E)  None of these

    Correct Answer: D

    Solution :

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


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