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    If , then the value of is:
    Question

    If , then the value of is:

    A.

    113682

    B.

    103682

    C.

    103882

    D.

    103862

    Correct option is B

    Given:

    ​We are given x+1x=7x + \frac{1}{x} = 7 ​​

    Solution:

    Square both sides of x+1x=7:x + \frac{1}{x} = 7 :

    (x+1x)2=72\left( x + \frac{1}{x} \right)^2 = 7^2​​

    x2+2+1x2=49x^2 + 2 + \frac{1}{x^2} = 49​​

    x2+1x2=47x^2 + \frac{1}{x^2} = 47​​

    Square again to find x4+1x4:x^4 + \frac{1}{x^4} :​​

    (x2+1x2)2=472\left( x^2 + \frac{1}{x^2} \right)^2 = 47^2​​

    x4+2+1x4=2209x^4 + 2 + \frac{1}{x^4} = 2209​​

    x4+1x4=2207x^4 + \frac{1}{x^4} = 2207​​

    Use the relation for x6+1x6x^6 + \frac{1}{x^6}​​

    (x2+1x2)(x4+1x4)=x6+1x6+x2+1x2\left( x^2 + \frac{1}{x^2} \right) \left( x^4 + \frac{1}{x^4} \right) = x^6 + \frac{1}{x^6} + x^2 + \frac{1}{x^2}​​

    47×2207=x6+1x6+4747 \times 2207 = x^6 + \frac{1}{x^6} + 47​​

    103729=x6+1x6+47103729 = x^6 + \frac{1}{x^6} + 47​​

    x6+1x6=103682x^6 + \frac{1}{x^6} = 103682​​

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