RAJASTHAN ­ PET Rajasthan PET Solved Paper-2007

  • question_answer
    If\[1,\omega \]and\[{{\omega }^{2}}\]are the cube roots of unity, then the roots of the equation\[{{(x-1)}^{3}}+8=0\]are

    A)  \[-1,-1+2\omega ,-1-2{{\omega }^{2}}\]

    B)  \[-1,-1,-1\]

    C)  \[-1,1-2\omega ,1-2{{\omega }^{2}}\]

    D)  \[-1,1+2\omega ,1+2{{\omega }^{2}}\]

    Correct Answer: C

    Solution :

     Given, \[{{(x-1)}^{3}}+8=0\] \[\Rightarrow \] \[{{(x-1)}^{3}}=-8\] \[\Rightarrow \] \[{{\left( \frac{x-1}{-2} \right)}^{3}}=1\] \[\Rightarrow \] \[\frac{x-1}{-2}={{(1)}^{1/3}}\] \[\Rightarrow \] \[\frac{x-1}{-2}=1,\omega ,{{\omega }^{2}}\] \[\Rightarrow \] \[x-1=-2,-2\omega ,-2{{\omega }^{2}}\] \[\Rightarrow \] \[x=-1,1-2\omega ,1-2{{\omega }^{2}}\]


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