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7th Class Mental Ability Algebraic Expressions Question Bank Algebra

  • question_answer
    If \[\mathbf{x -}\frac{\mathbf{1}}{\mathbf{x}}\mathbf{= 2}\], then find the value of\[{{\mathbf{x}}^{\mathbf{3}}}\mathbf{ -}\frac{\mathbf{1}}{{{\mathbf{x}}^{\mathbf{3}}}}\] .

    A) 14       

    B) 17

    C) 16             

    D) 15

    E) None of these

    Correct Answer: A

    Solution :

    Explanation \[{{x}^{3}}-\frac{1}{{{x}^{3}}}={{\left( x-\frac{1}{x} \right)}^{3}}+3\times (x)\times \left( \frac{1}{x} \right)\left( x-\frac{1}{x} \right)\] \[=\,\,\,{{2}^{3}}+3\,\,\times \,\,2=8+6=14.\]     


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