# Solve a calculus problem?

GROUPS:
 Consider the following code: \$Assumptions = Element[f, Reals] && Element[\[Beta], Reals] && Element[\[Alpha], Reals] && Element[n, Reals] && Element[\[Epsilon], Reals] && \[Alpha] > 0 && \[Beta] > 0 && \[Mu] > 0 && \[Epsilon] > 0 && f > 0 && n > 0 f := 1 - Exp[-\[Beta] (1 - Exp[-\[Alpha]\[Epsilon]])^n] DSolve[f''[\[Epsilon]] == 0, f[\[Epsilon]], \[Epsilon]] I get the following error message : DSolve::ivar: 1-E^(-(1-Power[<<2>>])^n \[Beta]) is not a valid variable. What is my mistake? What is the correct method?
3 months ago
2 Replies
 Daniel Lichtblau 1 Vote You gave f a value so it cannot be a dependent variable (the message pretty much states this). Maybe try Clear[f] before running the DSolve.
3 months ago
 Thanks. I am a newcomer to mathematica. Yes, your solution did not lead to the old error. But I still do not understand many things. You say that I gave f a value. I was just trying to define my function. Why did Clear not erase the definition?I will try again with a function where I know the answer. This will hopefully help me to learn what I should do. I should get x0 as the solution for f''[x]==0. The slope at this point should be U/(4*C). How do I get this with mathematica. How should I handle C[1] and C[2]? I don't understand what they mean.