CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2008

  • question_answer
    If\[\frac{5{{z}_{2}}}{11{{z}_{1}}}\]is purely imaginary, then the value of\[\left[ \frac{2{{z}_{1}}+3{{z}_{2}}}{2{{z}_{1}}-3{{z}_{2}}} \right]\]is

    A)  \[\frac{37}{33}\]                                             

    B)  \[2\]

    C)  1                            

    D)  \[3\]

    E)  \[\frac{33}{37}\]

    Correct Answer: C

    Solution :

    Since,                   \[\frac{5{{z}_{2}}}{11{{z}_{1}}}=iy\]                               (say) or            \[\frac{{{z}_{2}}}{{{z}_{1}}}=\frac{11}{5}iy\] Now,     \[\left| \frac{2{{z}_{1}}+3{{z}_{2}}}{2{{z}_{1}}-3{{z}_{2}}} \right|=\frac{\left| 2+3\frac{{{z}_{2}}}{{{z}_{1}}} \right|}{\left| 2-3\frac{{{z}_{2}}}{{{z}_{1}}} \right|}\]                                 \[=\frac{\left| 2+\frac{33}{5}iy \right|}{\left| 2-\frac{33}{5}iy \right|}=1\]


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