CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2007

  • question_answer
    The  magnitude  and  amplitude  of \[\frac{(1+i\sqrt{3})(2+2i)}{(\sqrt{3}-i)}\]are respectively

    A)  \[2,\frac{3\pi }{4}\]                       

    B)  \[4,\frac{3\pi }{4}\]

    C)  \[2\sqrt{2},\frac{\pi }{4}\]          

    D)         \[2\sqrt{2},\frac{\pi }{2}\]

    E)  \[2\sqrt{2},\frac{3\pi }{4}\]

    Correct Answer: E

    Solution :

    \[\frac{(1+i\sqrt{3})(2+2i)}{(\sqrt{3}-i)}=\frac{2+2i+2\sqrt{3}i-2\sqrt{3}}{(\sqrt{3}-i)}\] \[=\frac{\{(2-2\sqrt{3})+2i(1+\sqrt{3})\}}{(\sqrt{3}-i)}\times \frac{(\sqrt{3}+i)}{(\sqrt{3}+i)}\] \[=\frac{2\sqrt{3}-6+2i-2\sqrt{3}i+2\sqrt{3}i+6i-2-2\sqrt{3}}{3+1}\] \[=\frac{-8+8i}{4}=-2+2i\] \[\therefore \]Magnitude of\[\frac{(1+i\sqrt{3})(2+2i)}{(\sqrt{3}-i)}\]                                 \[=\sqrt{4+4}=2\sqrt{2}\] and amplitude of\[\frac{(1+i\sqrt{3})(2+2i)}{(\sqrt{3}-i)}\]                                 \[={{\tan }^{-1}}\left( \frac{2}{-2} \right)=\frac{3\pi }{4}\]


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