f[x_] := x^2 + c;(adsbygoogle = window.adsbygoogle || []).push({});

y = Solve[f'[f[x]] == 1, x, Reals]

output:

{{x -> ConditionalExpression[Root[-1 + 4 c #1 + 4 #1^3 &, 1],

c > -(3/4) || c < -(3/4)]}, {x ->

ConditionalExpression[Root[-1 + 4 c #1 + 4 #1^3 &, 2],

c < -(3/4)]}, {x ->

ConditionalExpression[Root[-1 + 4 c #1 + 4 #1^3 &, 3],

c < -(3/4)]}}

Then i want to put the solutions in terms of c which doesnt work with:

Eliminate[c == -x - x^2 && x == y[[1]], x]

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# Solving an equation with conditional solutions

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