JEE Main & Advanced JEE Main Paper (Held On 11 April 2014)

  • question_answer
    If \[{{z}_{1}},{{z}_{2}}\]and \[{{z}_{3}},{{z}_{4}}\]are 2 pairs of complex conjugate numbers, then \[\arg \left( \frac{{{z}_{1}}}{{{z}_{4}}} \right)+\arg \left( \frac{{{z}_{2}}}{{{z}_{3}}} \right)\]equals:   [JEE Main Online Paper ( Held On 11 Apirl  2014 )

    A) 0                                             

    B) \[\frac{\pi }{2}\]

    C) \[\frac{3\pi }{2}\]                                            

    D) \[\pi \]

    Correct Answer: A

    Solution :

                    Consider \[\arg \left( \frac{{{z}_{1}}}{{{z}_{4}}} \right)+\arg \left( \frac{{{z}_{2}}}{{{z}_{3}}} \right)\] \[=\arg ({{z}_{1}})-arg({{z}_{4}})+arg({{z}_{2}})-arg({{z}_{3}})\] \[=\arg ({{z}_{1}})+arg({{z}_{2}}))-(arg({{z}_{3}})+arg({{z}_{4}}))\] given\[\left( \begin{matrix}    {{z}_{2}}={{\overline{z}}_{1}}\And   \\    {{z}_{4}}={{\overline{z}}_{3}}  \\ \end{matrix} \right)\] \[=(\arg \,({{z}_{1}})+arg({{\overline{z}}_{1}}))-(arg({{z}_{3}})+arg({{\overline{z}}_{3}}))\] \[\left\{ \begin{align}   & also\,(\arg ({{\overline{z}}_{1}})=-arg({{z}_{1}}) \\  & arg({{\overline{z}}_{3}})=-arg({{z}_{3}}) \\ \end{align} \right\}\] \[=\,(\arg \,({{z}_{1}})-arg({{z}_{1}}))-(arg({{z}_{3}})-arg({{z}_{3}}))\] \[=0-0=0\]


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