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

  • question_answer
    If \[z=\frac{1+i\sqrt{3}}{\sqrt{3}+i},\] then\[{{(\bar{z})}^{100}}\] lies in [AMU 1999]

    A) I quadrant

    B) II quadrant

    C) III quadrant

    D) IV quadrant

    Correct Answer: C

    Solution :

    \[z=\frac{1+i\sqrt{3}}{\sqrt{3}+i}\]\[\Rightarrow z=\frac{1+i\sqrt{3}}{\sqrt{3}+i}\times \frac{\sqrt{3}-i}{\sqrt{3}-i}\] \[\Rightarrow \] \[z=\frac{\sqrt{3}+3i-i+\sqrt{3}}{3+1}\]\[=\frac{2(\sqrt{3}+i)}{4}\] \[\Rightarrow \]  \[z=\frac{\sqrt{3}+i}{2}=\left[ \cos \frac{\pi }{6}+i\sin \frac{\pi }{6} \right]\] Now \[\bar{z}=\cos \frac{\pi }{6}-i\sin \frac{\pi }{6}\] Þ  \[{{(\bar{z})}^{100}}={{\left[ \cos \frac{\pi }{6}-i\sin \frac{\pi }{6} \right]}^{100}}\] Þ  \[{{(\bar{z})}^{100}}=\cos \frac{50\,\pi }{3}-i\sin \frac{50\,\pi }{3}\]\[=\,\cos \frac{2\pi }{3}-i\sin \frac{2\pi }{3}\] \[{{(\bar{z})}^{100}}\] lies in III quadrant.


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