CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2004

  • question_answer
    If\[\frac{2{{z}_{1}}}{3{{z}_{2}}}\]is a purely imaginary, then\[\left| \frac{{{z}_{1}}-{{z}_{2}}}{{{z}_{1}}+{{z}_{2}}} \right|\]is:

    A)  \[\frac{2}{3}\]                                  

    B)  \[\frac{3}{2}\]

    C)  \[\frac{4}{9}\]                  

    D)         \[1\]

    E)  \[\frac{9}{4}\]

    Correct Answer: D

    Solution :

    \[\because \]\[\frac{2{{z}_{1}}}{3{{z}_{2}}}\]is purely imaginary \[\Rightarrow \]               \[\frac{2{{z}_{1}}}{3{{z}_{2}}}=ki\]where \[k\in R\] \[\Rightarrow \]               \[\frac{{{z}_{1}}}{{{z}_{2}}}=\frac{3}{2}ki\] Now, \[\left| \frac{{{z}_{1}}-{{z}_{2}}}{{{z}_{1}}+{{z}_{2}}} \right|=\left| \frac{\frac{{{z}_{1}}}{{{z}_{2}}}-1}{\frac{{{z}_{1}}}{{{z}_{2}}}+1} \right|=\left| \frac{3ki-2}{3ki+2} \right|\]                 \[=1\]


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