CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2008

  • question_answer
    If\[{{(\sqrt{5}+\sqrt{3}i)}^{33}}={{2}^{49}}z,\]then modulus of the complex number z is equal to

    A)  1                                            

    B)  \[\sqrt{2}\]

    C)  \[2\sqrt{2}\]                     

    D)         4

    E)  8

    Correct Answer: B

    Solution :

    Given, \[{{(\sqrt{5}+\sqrt{3}i)}^{33}}={{2}^{49}}z\] Let\[\sqrt{5}=r\cos \theta ,\sqrt{3}=r\sin \theta \] \[\therefore \]  \[{{r}^{2}}=5+3\] \[\Rightarrow \]               \[r=2\sqrt{2}\] \[\therefore \]  \[{{(r\cos \theta +ir\sin \theta )}^{33}}={{2}^{49}}z\] \[\Rightarrow \]               \[|{{r}^{33}}(cos33\theta +i\sin 33\theta )=|{{2}^{49}}z|\] \[\Rightarrow \]               \[{{(2\sqrt{2})}^{33}}|\cos 33\theta +i\sin 33\theta |={{2}^{49}}|z|\] \[\Rightarrow \]               \[{{2}^{\frac{99}{2}}}(1)={{2}^{49}}|z|\] \[\Rightarrow \]               \[|z|={{2}^{\frac{99}{2}-49}}\] \[\Rightarrow \]               \[|z|=\sqrt{2}\]


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