CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2004

  • question_answer
    \[\tan \left[ i\log \left( \frac{a-ib}{a+ib} \right) \right]\]is equal to:

    A)  \[ab\]                  

    B)         \[\frac{2ab}{{{a}^{2}}-{{b}^{2}}}\]

    C)  \[\frac{{{a}^{2}}-{{b}^{2}}}{2ab}\]          

    D)         \[\frac{2ab}{{{a}^{2}}+{{b}^{2}}}\]

    E)  \[{{a}^{2}}+{{b}^{2}}\]

    Correct Answer: B

    Solution :

    \[\because \] \[\log \left( \frac{a-ib}{a+ib} \right)=\log (a-ib)-\log (a+ib)\] \[=-2i{{\tan }^{-1}}\left( \frac{b}{a} \right)\] \[\therefore \]  \[-i\log \left( \frac{a-ib}{a+ib} \right)=2{{\tan }^{-1}}\left( \frac{b}{a} \right)\]                                 \[={{\tan }^{-1}}\left( \frac{2ab}{{{a}^{2}}-{{b}^{2}}} \right)\] \[\Rightarrow \] \[\tan \left[ i\log \left( \frac{a-ib}{a+ib} \right) \right]=\frac{2ab}{{{a}^{2}}-{{b}^{2}}}\]


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