JEE Main & Advanced Mathematics Complex Numbers and Quadratic Equations Question Bank Conjugate, Modulus and Argument of complex number

  • question_answer
    If \[{{(\sqrt{8}+i)}^{50}}={{3}^{49}}(a+ib)\] then \[{{a}^{2}}+{{b}^{2}}\] is [Kerala (Engg.) 2005]

    A) 3

    B) 8

    C) 9

    D) \[\sqrt{8}\]

    E) 4

    Correct Answer: C

    Solution :

    \[{{(\sqrt{8}+i)}^{50}}={{3}^{49}}(a+ib)\] Taking modulus and squaring on both sides, we get \[{{(8+1)}^{50}}={{3}^{98}}({{a}^{2}}+{{b}^{2}})\] \[{{9}^{50}}={{3}^{98}}({{a}^{2}}+{{b}^{2}})\] \[{{3}^{100}}={{3}^{98}}({{a}^{2}}+{{b}^{2}})\] Þ \[({{a}^{2}}+{{b}^{2}})=9\].


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