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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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