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9th Class Mathematics Polynomials Question Bank Polynomials

  • question_answer
    If \[\mathbf{3x}+\frac{1}{\mathbf{3x}}=\mathbf{3}\], then the value of \[27{{x}^{3}}+\frac{1}{27{{x}^{3}}}\] is

    A)  -52                  

    B)  52             

    C)  18         

    D)  -18

    Correct Answer: C

    Solution :

    (c): \[{{\left( 3x+\frac{1}{3x} \right)}^{3}}=27{{x}^{3}}+\frac{1}{27{{x}^{3}}}+3\left( 3x+\frac{1}{3x} \right)\] \[{{\left( 3 \right)}^{3}}=27{{x}^{3}}+\frac{1}{27{{x}^{3}}}+3\left( 3x+\frac{1}{3x} \right)\] \[\therefore 27{{x}^{3}}+\frac{1}{27{{x}^{3}}}=27-9=18\]                           


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