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Power and Inverse Power Sum (Posted on 2024-08-13) Difficulty: 3 of 5
If x+x-1=1, then find the value of:
(x+1)2 + (x+1)-2

No Solution Yet Submitted by K Sengupta    
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Some Thoughts I think it's ... | Comment 1 of 4
x + 1/x = 1
Can solve as quadratic:
x^2 - x + 1 = 0
x = (1 ± √3 i)/2

Or rearrange to get x^2 = x-1
and use to reduce the power.
then (x+1)^2 --> x^2 + 2x + 1 = 3x

So now find 3x + 1/(3x)
Choose x = (1 + √3 i)/2

Find 3(1 + √3 i)/2 + 2/3(1 + √3 i)
= 3(1 + √3 i)/2 + 2(1 - √3 i)/3(1 + √3 i)(1 - √3 i)
= 3(1 + √3 i)/2 + 2(1 - √3 i)/3(1+3)
= 3(1 + √3 i)/2 + (1 - √3 i)/6
= 5/3 + (4/3)√3 i

Although double checking on Wolfram Alpha gives a different result which, when I simplified it, worked out to the conjugate of my answer.  So either I made a math error or Wolfram Alpha did.

  Posted by Larry on 2024-08-14 08:22:08
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