Railways Sample Paper RRBs Assistant Loco Pilot and Technician CBT STAGE-I Sample Paper-15

  • question_answer
    If\[x-\frac{1}{x}=\]then value of\[{{x}^{4}}+\frac{1}{{{x}^{4}}}\]is equal to

    A)  4                    

    B)  8

    C)  12                   

    D)  34

    Correct Answer: D

    Solution :

    \[\because x-\frac{1}{2}=2\] \[\Rightarrow \]   \[{{\left( x-\frac{1}{2} \right)}^{2}}=4\] \[\Rightarrow \]   \[{{x}^{2}}-2x.\frac{1}{2}+\frac{1}{{{x}^{2}}}=4\] \[\Rightarrow \]   \[{{x}^{2}}+\frac{1}{{{x}^{2}}}=4+2=6\] \[\Rightarrow \]        \[{{x}^{2}}+\frac{1}{{{x}^{2}}}=6\] \[\Rightarrow \]   \[{{\left( {{x}^{2}}+\frac{1}{{{x}^{2}}} \right)}^{2}}={{(6)}^{2}}\] \[\Rightarrow \]   \[{{x}^{4}}+2+\frac{1}{{{x}^{4}}}=36\] \[\Rightarrow \]   \[{{x}^{4}}+\frac{1}{{{x}^{4}}}=36-2\] \[\therefore \,\,\]  \[{{x}^{4}}+\frac{1}{{{x}^{4}}}=34\]


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