JEE Main & Advanced Mathematics Complex Numbers and Quadratic Equations Question Bank De Moivre's theorem and Roots of unity

  • question_answer
    The \[{{n}^{th}}\]roots of unity are in [Orissa JEE 2004]

    A) A.P.

    B) G.P.

    C) H.P.

    D) None of these

    Correct Answer: B

    Solution :

    \[{{x}^{n}}=1=(\cos 0+i\sin {{0}^{o}})=\cos 2r\pi +i\sin 2r\pi ={{e}^{i2r\pi }}\] Þ \[x={{e}^{i(2r\pi /n)}},r=0,\,1,\,2\]??.. Obviously the roots are\[1,{{e}^{2\pi i/n}},{{e}^{4\pi i/n}}\]...... which are obviously in G.P. with common ratio\[{{e}^{2\pi i/n}}\].


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