I am having trouble understanding it, first of all, what is x? Are x's coefficients of this polynomial we are looking for? This would mean that the polynomial is of degree $n-1$ because it has n coefficients? Second of all is this +- notation equal to module? And another question, can anyone give me a simple example of those polynomials and function so I can understand it better? Any help appreciated thanks. :) My example: $f(t)=|t|$ , $t\in[-1,1]$, if p(x,t) was of degree less or equal to 2 we would be looking for is $p(x,t))= \frac{1}{2}$, because of alternans theorem, but in our case it is the polynomial of a degree $(n-1)$ so what is an optimal polynomial?...