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SSC Sample Paper SSC CGL - Sample Paper-7

  • question_answer
    If \[x={{2}^{\frac{1}{3}}}+{{2}^{\frac{1}{3}}},\] then the value of \[2{{x}^{3}}-6x\] will be    

    A)  5        

    B)  6

    C)  8                                

    D)  10

    Correct Answer: A

    Solution :

    \[x={{2}^{1/3}}+{{2}^{-1/3}}\] On cubing both sides, we get             \[{{x}^{3}}=2+{{2}^{-1}}+3({{2}^{1/3}}+{{2}^{-1/3}})\] \[\Rightarrow \]   \[{{x}^{3}}=\frac{4+1}{2}+3x\] \[\Rightarrow \]   \[2{{x}^{2}}=5+6x\] \[\Rightarrow \]   \[2{{x}^{3}}-6x=5\]               


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