data={{1,2},{4,11.2},{5,10},{2,3}};
Print[ListPlot[data,Mesh->Automatic,PlotRange->All]];
Deltax=0.1;
ilast=IntegerPart[5.5/Deltax];
f[xdum_]=Fit[data,{1,x,x^2,x^3,x^4},x]/.{x->xdum};
Print[f[x]];
tf=Table[{i*Deltax,f[i*Deltax]},{i,0,ilast}];
ListPlot[{tf,data},PlotStyle->{Red,Blue}]
(*Plot[f[x],{x,0,6}]*)