1. The problem statement, all variables and given/known data Let f(x)=1-x-x3. Find all the real values of x satisfying the inequality, 1-f(x)-f3(x)>f(1-5x). 2. Relevant equations 3. The attempt at a solution I honestly don't know how to start with this one. Substituting f(x) directly in the inequality doesn't look like a good idea. I need a few hints to begin with. Any help is appreciated. Thanks!