CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2005

  • question_answer
    If\[z=r{{e}^{i\theta }},\]then\[|{{e}^{iz}}|\]is equal to:

    A)  \[1\]                    

    B)         \[{{e}^{2r\sin \theta }}\]

    C)  \[{{e}^{r\sin \theta }}\]               

    D)         \[r{{e}^{\sin \theta }}\]

    E)  \[{{e}^{-r\sin \theta }}\]

    Correct Answer: E

    Solution :

    If\[z=r{{e}^{i\theta }}=r(\cos \theta +i\sin \theta )\] \[\Rightarrow \]               \[iz=ir(\cos \theta +i\sin \theta )\]                 \[=-r\sin \theta +i\,r\,\cos \theta \] \[\therefore \]  \[{{e}^{iz}}={{e}^{-r\sin \theta +r\,i\,\cos \theta }}\]                 \[|{{e}^{iz}}|=|{{e}^{-r\sin \theta }}||{{e}^{ir\cos \theta }}|\]                 \[={{e}^{-r\sin \theta }}|{{e}^{ir\cos \theta }}|\] \[={{e}^{-r\sin \theta }}[{{\{{{\cos }^{2}}(r\cos \theta )+{{\sin }^{2}}(r\,\cos \theta )\}}^{1/2}}]\] \[\therefore \]  \[|{{e}^{iz}}|={{e}^{-r\sin \theta }}\]


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