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    ​If x−1x=3, then the value of x4+1x4 is:\text{If } x - \frac{1}{x} = 3, \text{ then the value of } x^4 + \frac{1}{x
    Question

    If x1x=3, then the value of x4+1x4 is:\text{If } x - \frac{1}{x} = 3, \text{ then the value of } x^4 + \frac{1}{x^4} \text{ is:}​​

    A.

    19

    B.

    196

    C.

    176

    D.

    119

    Correct option is D

    Given:

    x1x=3x-\dfrac{1}{x}=3​​

    Formula Used:

    (x1x)2=x2+1x22(x-\dfrac{1}{x})^2=x^2+\dfrac{1}{x^2}-2​​

    (x2+1x2)2=x4+1x4+2\left(x^2+\dfrac{1}{x^2}\right)^2=x^4+\dfrac{1}{x^4}+2​​

    Solution:
    (x1x)2=32=9 x2+1x2=9+2=11(x-\dfrac{1}{x})^2=3^2=9 \implies x^2+\dfrac{1}{x^2}=9+2=11​​
    (x2+1x2)2=112=121=x4+1x4+2\left(x^2+\dfrac{1}{x^2}\right)^2=11^2=121= x^4+\dfrac{1}{x^4}+2​​
    x4+1x4=1212=119x^4+\dfrac{1}{x^4}=121-2=119​​

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