8th Class Mathematics Algebraic Expressions Question Bank Algebraic Expressions & Identities

  • question_answer
    If \[{{\mathbf{a}}^{\mathbf{2}}}+\frac{1}{{{\mathbf{a}}^{\mathbf{2}}}}=\mathbf{14}\]find the value of \[{{x}^{\mathbf{2}}}+\frac{1}{{{x}^{\mathbf{2}}}}\]

    A)  2                                

    B)  4              

    C)  \[2\sqrt{3}\]  

    D) \[\sqrt{3}\]

    Correct Answer: C

    Solution :

    (c): \[={{a}^{2}}+\frac{1}{{{a}^{2}}}=14={{a}^{2}}-2.a.\frac{1}{a}+\frac{1}{{{a}^{2}}}=14-2\] \[\Rightarrow {{\left( a-\frac{1}{a} \right)}^{2}}=12\] \[\Rightarrow a-\frac{1}{a}=\sqrt{12}=2\sqrt{3}\].          


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