9th Class Mathematics Polynomials Question Bank Polynomials

  • question_answer
    If \[{{\left( \mathbf{a+}\frac{\mathbf{1}}{\mathbf{a}}\mathbf{~} \right)}^{\mathbf{2}}}\mathbf{=3}\], then the value of \[{{\mathbf{a}}^{\mathbf{206}}}\mathbf{+}{{\mathbf{a}}^{\mathbf{200}}}\mathbf{+}{{\mathbf{a}}^{\mathbf{90}}}\mathbf{+}{{\mathbf{a}}^{\mathbf{84}}}\mathbf{+}{{\mathbf{a}}^{\mathbf{18}}}\mathbf{+}{{\mathbf{a}}^{\mathbf{12}}}\mathbf{+}{{\mathbf{a}}^{\mathbf{6}}}\mathbf{+1}\]is

    A)  0             

    B)  1

    C)  84                               

    D)  206

    Correct Answer: A

    Solution :

    (a): \[{{\left( a+\frac{1}{a} \right)}^{2}}=3\,\,\,\Rightarrow a+\frac{1}{a}=\sqrt{3}\] On cubing both sides, \[{{a}^{3}}+\frac{1}{{{a}^{3}}}+3\left( a+\frac{1}{a} \right)=3\sqrt{3}\] \[\Rightarrow {{a}^{3}}+\frac{1}{{{a}^{3}}}=3\sqrt{3}-3\sqrt{3}=0\,\,\,\,\,\,\Rightarrow {{a}^{6}}+1=0\] \[\therefore {{a}^{200}}+{{a}^{200}}+{{a}^{90}}+{{a}^{84}}+{{a}^{18}}+{{a}^{12}}+{{a}^{6}}+1\] \[={{a}^{200}}\left( {{a}^{6}}+1 \right)+{{a}^{84}}\left( {{a}^{6}}+1 \right)+{{a}^{12}}\left( {{a}^{6}}+1 \right)+\left( {{a}^{6}}+1 \right)\]\[=0\]            


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