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

  • question_answer
    If \[{{\mathbf{a}}^{\mathbf{2}}}+\frac{1}{{{\mathbf{a}}^{\mathbf{2}}}}=27\] find the value of \[\left( {{a}^{3}}-\frac{1}{{{a}^{3}}} \right)\]

    A)  120                             

    B)  140   

    C)  100                             

    D)  110

    Correct Answer: B

    Solution :

    (b): questions 14 to 16 are problems of similar type. They are based on the formula \[{{\left( a+\frac{1}{a} \right)}^{2}}={{a}^{2}}+2.a.\frac{1}{a}+\frac{1}{{{a}^{2}}}={{a}^{2}}+2+\frac{1}{{{a}^{2}}}\] or, \[{{\left( a-\frac{1}{a} \right)}^{2}}={{a}^{2}}-2+\frac{1}{{{a}^{2}}}\].


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