JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2007

  • question_answer
        Let\[z,w\]be complex numbers such that \[\overline{z}+i\overline{w}=0\]and arg\[zw=\pi \]Then arg z equals:

    A)  \[\frac{\pi }{4}\]                             

    B)  \[\frac{\pi }{2}\]

    C)  \[\frac{3\pi }{4}\]                                           

    D)  \[\frac{5\pi }{4}\]

    Correct Answer: C

    Solution :

                    Since \[\overline{z}+i\overline{w}=0\Rightarrow \overline{z}=i\overline{w}\] \[\Rightarrow \]               \[z=iw\Rightarrow w=-iz\] Also arg\[(zw)=\pi \] \[\Rightarrow \]               \[\arg (-i{{z}^{2}})=\pi \] \[\Rightarrow \]               \[\arg (-i)+2\arg (z)=\pi \] \[\Rightarrow \]               \[-\frac{\pi }{2}+2\arg (z)=\pi \]                                 \[(\because \arg (-i)=-\frac{\pi }{2})\] \[\Rightarrow \]               \[2\arg (z)=\frac{3\pi }{2}\] \[\Rightarrow \]               \[\arg (z)=\frac{3\pi }{4}\]


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