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If x² - 3x + 1 = 0 then what is the value of x2+x+1x+1x2x² + x + \frac{1}{x} + \frac{1}{x²}x2+x+x1​+x21​​?
Question

If x² - 3x + 1 = 0 then what is the value of x2+x+1x+1x2x² + x + \frac{1}{x} + \frac{1}{x²}​?

A.

7

B.

8

C.

9

D.

10

Correct option is D

Given:

x² - 3x + 1 = 0

Formula Used:

(a+b)2=a2+b2+2ab(a+b)^2 = a^2 + b^2 +2ab​​

Solution:

x² - 3x + 1 = 0

Divide by x both side:

x2x3xx+1x=0\frac{x^2}{x} - \frac{3x}{x} + \frac{1}{x} = 0

x3+1x=0x - 3 + \frac{1}{x} = 0

​​x+1x=3x + \frac{1}{x} = 3  ......(1).

Squaring both side:

(x+1x)2=32\left(x + \frac{1}{x}\right)^2 = 3^2

x2+1x2+2=9x^2 + \frac{1}{x^2} + 2 = 9

​​​x2+1x2=92x^2 + \frac{1}{x^2} = 9 - 2

x2+1x2=7x^2 + \frac{1}{x^2} = 7 ....(2)

Add equation (1) and (2);
x2+1x2+x+1x=3+7x^2 + \frac{1}{x^2}+ x + \frac{1}{x} = 3 + 7

x2+x+1x+1x2=10x^2 + x + \frac{1}{x} + \frac{1}{x^2}= 10

Thus, the correct answer is (d).

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