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If x + 1x\frac 1xx1​​= –1, then compute: x4+1x4+2x2+2x2x^4 + \frac{1}{x^4} + 2x^2 + \frac{2}{x^2}x4+x41​+2x2+x22​​​
Question

If x + 1x\frac 1x​= –1, then compute: x4+1x4+2x2+2x2x^4 + \frac{1}{x^4} + 2x^2 + \frac{2}{x^2}​​

A.

–3

B.

3

C.

4

D.

–4

Correct option is A

Given:
x+1x=1x + \frac{1}{x} = -1​​
Formula Used:
(x+1x)2=x2+1x2+2(x2+1x2)2=x4+1x4+2\left(x + \frac{1}{x}\right)^2 = x^2 + \frac{1}{x^2} + 2 \\\left(x^2 + \frac{1}{x^2}\right)^2 = x^4 + \frac{1}{x^4} + 2​​
Solution:

x+1x=1Squaring both sides:(x+1x)2=(1)2x2+1x2+2=1x2+1x2=1Squaring again:(x2+1x2)2=(1)2x4+1x4+2=1x4+1x4=1Now evaluate:x4+1x4+2x2+2x2=(1)+2(1)=3x + \frac{1}{x} = -1\\[4pt]\text{Squaring both sides:} \\\left(x + \frac{1}{x}\right)^2 = (-1)^2 \\x^2 + \frac{1}{x^2} + 2 = 1 \\x^2 + \frac{1}{x^2} = -1\\[6pt]\text{Squaring again:} \\\left(x^2 + \frac{1}{x^2}\right)^2 = (-1)^2 \\x^4 + \frac{1}{x^4} + 2 = 1 \\x^4 + \frac{1}{x^4} = -1\\[6pt]\text{Now evaluate:} \\x^4 + \frac{1}{x^4} + 2x^2 + \frac{2}{x^2} \\= (-1) + 2(-1) \\= -3

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