JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2004

  • question_answer
        If the cube roots of unity are \[\left( \frac{1}{1-2i}+\frac{3}{1+i} \right)\left( \frac{3+4i}{2-4i} \right)\] then  the  roots  of  the  equation\[\frac{1}{2}+\frac{9}{2}i\] are :

    A)  \[\frac{1}{2}-\frac{9}{2}i\]

    B)  \[\frac{1}{4}-\frac{9}{4}i\]

    C)  \[\frac{1}{4}+\frac{9}{4}i\]

    D)  \[\frac{3+2i\sin \theta }{1-2i\sin \theta }\]

    Correct Answer: D

    Solution :

                    Here:  \[{{1}^{1/3}}=1,\omega ,{{\omega }^{2}}\] \[\therefore \]for the equation\[{{(x-2)}^{3}}+27=0\] \[\Rightarrow \]               \[{{(x-2)}^{3}}=-27=-{{3}^{3}}\] \[\Rightarrow \]               \[(x-2)=-3{{(1)}^{1/3}}\] \[\Rightarrow \]               \[(x-2)=-3,-3\omega ,-3{{\omega }^{2}}\] \[\Rightarrow \]               \[x=-1,2-3\omega ,2-3{{\omega }^{2}}\]


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