# Finding ranges of a parameter for which a function is always positive

I have a complex function of a single variable expressed in analytical form, which also depends on a parameter. I would like to have Mathematica show me for which values of the parameter the real part of the second derivative of the function is always positive.

Strictly speaking, maybe I have given too much detail here, the real part/derivative stuff is ultimately inessential, what I want Mathematica to do is to tell me for what choices of a parameter a real function is positive everywhere. I hope the question is clear, though.

• If you need a numerical approximation for a function that can't be treated analytically, you can use RegionPlot. – Szabolcs May 24 '12 at 8:16

For example, Reduce:

Reduce[
ForAll[x, α*x^2 + β*x + γ > 0],
{α, β, γ},
Reals
]


which looks like this: tells us that $\alpha x^2+\beta x+\gamma>0$ for all $x$ if these conditions hold: Resolve[
ForAll[x, α*x^2 + β*x + γ > 0] && x ∈ Reals,
Reals
] • That's exactly what I was looking for! Thank you! – zakk May 22 '12 at 22:00