J & K CET Engineering J and K - CET Engineering Solved Paper-2006

  • question_answer
    The argument of \[\frac{1+i\sqrt{3}}{1-i\sqrt{3}}\] is

    A)  \[2\pi /3\]                                 

    B)  \[\pi /3\]

    C)  \[-\pi /3\]          

    D)  \[-2\pi /3\]

    Correct Answer: A

    Solution :

    \[\frac{1+i\sqrt{3}}{1-i\sqrt{3}}=\frac{1+i\sqrt{3}}{1-i\sqrt{3}}\times \frac{1+i\sqrt{3}}{1+i\sqrt{3}}\] \[=\frac{{{(1+i\sqrt{3})}^{2}}}{1+3}\] \[=\frac{1-3+2i\sqrt{3}}{4}\] \[=-\frac{1}{2}+\frac{i\sqrt{3}}{2}\] Here;   \[x=-\frac{1}{2},\,y=\frac{\sqrt{3}}{2}\] \[\therefore \]  \[\tan \theta =\frac{y}{x}=\frac{\sqrt{3}}{2}\times \frac{2}{-1}=-\sqrt{3}=-\tan \frac{\pi }{3}\] \[\Rightarrow \] \[\tan \theta =\tan \left( \pi -\frac{\pi }{3} \right)\] \[\Rightarrow \]                       \[\theta =\frac{2\pi }{3}\]


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