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  • $\begingroup$ I don't see any "simplification" going on here. You just solve for the two roots and insert them into the expression: (2*x1^2 + 3*x1*x2 + 2*x2^2)/(4 x1^2*x2 + 4*x2^2*x1) /. Thread[{x1, x2} -> SolveValues[2 x^2 + 5 x - 7 == 0, x]]. What would you want to go any other way? $\endgroup$ Commented Oct 16, 2024 at 17:22
  • $\begingroup$ @Domen: Thank yiu for the interest to the question. Sorry, I don't understand your "I don't see any "simplification" going on here". The point of the question is as follows. I expected the conditions 2 x1^2 + 5 x1 - 7 == 0 && 2 x2^2 + 5 x2 - 7 == 0 && x1 < x2 are enough for the simplification, but it is not so. Also think about the analog of the question for cubic, say to simplify a symmetric expression formed by x1,x2,x3 which are rhe roots of a cubic. Don't hesitate to ask forv further explanation in need $\endgroup$ Commented Oct 16, 2024 at 17:46
  • $\begingroup$ @Domen: (2*x1^2 + 3*x1*x2 + 2*x2^2 + 3 x2*x3 + 2 x3^2 + 3 x1*x3)/(4 x1^2*x2 + 4 x1^2*x3 + 4*x2^2*x1 + 4 x2^2*x3 + 4 x3^2*x1 + 4 x3^2*x2) /. Thread[{x1, x2, x3} -> SolveValues[2 x^3 + 5 x - 7 == 0, x]] outputs (2 + 3/2 (-1 - I Sqrt[13]) + 1/2 (-1 - I Sqrt[13])^2 + 3/2 (-1 + I Sqrt[13]) + 3/4 (-1 - I Sqrt[13]) (-1 + I Sqrt[13]) + 1/2 (-1 + I Sqrt[13])^2)/(2 (-1 - I Sqrt[13]) + (-1 - I Sqrt[13])^2 + 2 (-1 + I Sqrt[13]) + 1/2 (-1 - I Sqrt[13])^2 (-1 + I Sqrt[13]) + (-1 + I Sqrt[13])^2 + 1/2 (-1 - I Sqrt[13]) (-1 + I Sqrt[13])^2). $\endgroup$ Commented Oct 16, 2024 at 18:09
  • $\begingroup$ I have a doubt that approach works for seventh degree. $\endgroup$ Commented Oct 16, 2024 at 18:15
  • 2
    $\begingroup$ @user64494 MMa v12.2 evaluates your first codeline without problems to 16/35 $\endgroup$ Commented Oct 16, 2024 at 20:28