VIT Engineering VIT Engineering Solved Paper-2010

  • question_answer
    If \[z=\frac{1-i\sqrt{3}}{1+i\sqrt{3}},\]then arg (z) is

    A)  \[60{}^\circ \]

    B)  \[120{}^\circ \]

    C)  \[240{}^\circ \]

    D)  \[300{}^\circ \]

    Correct Answer: C

    Solution :

    \[z=\left( \frac{1-i\sqrt{3}}{1+i\sqrt{3}} \right)\] \[\Rightarrow \] \[z=\frac{1-i\sqrt{3}}{1+i\sqrt{3}}\times \frac{1-i\sqrt{3}}{1-i\sqrt{3}}\] \[\Rightarrow \] \[z=\frac{1-3-2\sqrt{3}i}{1+3}=\frac{-2-2\sqrt{3}i}{4}\] \[\Rightarrow \] \[z=-\frac{1}{2}-\frac{\sqrt{3}}{2}i\] \[\Rightarrow \] \[z=\cos 240{}^\circ -i\,\sin 240{}^\circ \] Thus, \[\arg \,(z)=240{}^\circ \]


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