S0[x_]:=(11/4)x-(3/4)x^3;
S1[x_]:=2+(x-1)/2-(9/4)(x-1)^2+(3/4)(x-1)^3
S[x_]=If[x<1,S0[x],S1[x]];
Plot[{S0[x],S1[x]},{x,0,2},PlotRange->{-2,3}]
Plot[S[x],{x,0,2},PlotRange->{-2,3}]