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Roots in modified fractions (Posted on 2024-05-19) Difficulty: 3 of 5
If x1,x2,x3 are the roots of equation x3-x-1=0 then compute

(2024+x1)/(2024-x1)+(2024+x2)/(2024-x2)+(2024+x3)/(2024-x3)

No Solution Yet Submitted by Danish Ahmed Khan    
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Solution Solution | Comment 1 of 3
I will let x,y,z be the three roots, and 2024 is generalized to k.
First I gave the big expression a common denominator and did some tedious algebra:
[3k^3 - (x+y+z)*k^2 - (xy+xz+yz)*k + 3xyz] / [k^3 - (x+y+z)*k^2 + (xy+xz+yz)*k - xyz]

Then from the given cubic equation xyz=1, xy+yz+xz=-1, and x+y+z=0.  Substitute these into the expression:
[3k^3 - 0*k^2 - -1*k + 3*1] / [k^3 - 0*k^2 + -1*k - 1]

Then we get a simplified form of [3k^3+k+3]/[k^3-k-1], then at k=2024 we have a value of [3*2024^3+2024+3]/[2024^3-2024-1] = 24874411499/8291467799

  Posted by Brian Smith on 2024-05-19 12:12:53
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