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If x+1xx + \frac{1}{x}x+x1​ = 4 , then find the value of x2+1x2x ^2+ \frac{1}{x^2}x2+x21​​​
Question

If x+1xx + \frac{1}{x} = 4 , then find the value of x2+1x2x ^2+ \frac{1}{x^2}​​

A.

16

B.

14

C.

12

D.

18

Correct option is B

Given: 

x+1x=4x+\frac{1}{x}=4​​

Solution:

The given equation: x+1x=4x+\frac{1}{x}=4 

​Square both sides of the equation: 

(x+1x)2=42(x+\frac{1}{x})^2=4^2 

x2+2×x×1x+1x2=16x^2+2\times x \times\frac{1}{x}+\frac{1}{x^2}=16 

x2+2+1x2=16x^2+2+\frac{1}{x^2}=16 

​Subtract 2 from both sides :  x2+1x2x^2+\frac{1}{x^2} 

x2+1x2=162x^2+\frac{1}{x^2}=16 -2​​

x2+1x2x^2+\frac{1}{x^2} =14

Thus, correct answer is (b) 14

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