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

  • question_answer
    The value of \[\frac{a+b\omega +c{{\omega }^{2}}}{b+c\omega +a{{\omega }^{2}}}+\frac{a+b\omega +c{{\omega }^{2}}}{c+a\omega +b{{\omega }^{2}}}\] will be [BIT Ranchi 1989; Orissa JEE 2003]

    A) 1

    B) - 1

    C) 2

    D) - 2

    Correct Answer: B

    Solution :

    Multiplying the numerator and denominator by \[\omega \] and \[{{\omega }^{2}}\] respectively I and II expressions \[=\frac{a+b\omega +c{{\omega }^{2}}}{b+c\omega +a{{\omega }^{2}}}+\frac{a+b\omega +c{{\omega }^{2}}}{c+a\omega +b{{\omega }^{2}}}\] \[=\frac{\omega (a+b\omega +c{{\omega }^{2}})}{(b\omega +c{{\omega }^{2}}+a)}+\frac{{{\omega }^{2}}(a+b\omega +c{{\omega }^{2}})}{(c{{\omega }^{2}}+a+a\omega )}=\omega +{{\omega }^{2}}=-1\]


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