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

  • question_answer
    If \[{{(1+i\sqrt{3})}^{9}}=a+ib,\] then \[b\] is equal to [RPET 1995]

    A) 1

    B) 256

    C) 0

    D) \[{{9}^{3}}\]

    Correct Answer: C

    Solution :

    \[1+i\sqrt{3}=2\left( \frac{1}{2}+i\frac{\sqrt{3}}{2} \right)=2\left[ \cos \frac{\pi }{3}+i\sin \frac{\pi }{3} \right]=2{{e}^{i\pi /3}}\] \ \[{{(1+i\sqrt{3})}^{9}}={{(2{{e}^{i\pi /3}})}^{9}}={{2}^{9}}.{{e}^{i(3\pi )}}\]                     \[={{2}^{9}}(\cos 3\pi +i\sin 3\pi )=-{{2}^{9}}\] \ \[a+ib={{(1+i\sqrt{3})}^{9}}=-{{2}^{9}}\];  \ \[b=0\].


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