8th Class Mathematics Sample Paper Mathematics Sample Paper - 5

  • question_answer
    If \[x-\frac{1}{x}=9\], then find the value \[{{x}^{2}}+\frac{1}{{{x}^{2}}}\].

    Answer:

    \[x-\frac{1}{x}=9\]
    Use the identity \[{{\left( ab \right)}^{2}}={{a}^{2}}+{{b}^{2}}2ab\]                                             
    \[{{\left( x-\frac{1}{x} \right)}^{2}}={{x}^{2}}+\frac{1}{{{x}^{2}}}-2\times (x)\times \left( \frac{1}{2} \right)\]
    \[{{(9)}^{2}}={{x}^{2}}+\frac{1}{{{x}^{2}}}-2\]
    \[81+2={{x}^{2}}+\frac{1}{{{x}^{2}}}\]       
    \[83={{x}^{2}}+\frac{1}{{{x}^{2}}}\]


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