s1[x_]=FourierSinSeries[x,x,1];

Plot[{s1[x], x},{x,0,Pi},PlotRange->{0,3.45},PlotStyle->Thick]

s2[x_]=FourierSinSeries[x,x,2];

Plot[{s2[x],x},{x,0,Pi},PlotRange->{0,3.45},PlotStyle->Thick]

s3[x_]=FourierSinSeries[x,x,3];

Plot[{s3[x],x},{x,0,Pi},PlotRange->{0,3.45},PlotStyle->Thick]

s4[x_]=FourierSinSeries[x,x,4];

Plot[{s4[x],x},{x,0,Pi},PlotRange->{0,3.45},PlotStyle->Thick]

s5[x_]=FourierSinSeries[x,x,5];

Plot[{s5[x],x},{x,0,Pi},PlotRange->{0,3.45},PlotStyle->Thick]

s6[x_]=FourierSinSeries[x,x,6];

Plot[{s6[x],x},{x,0,Pi},PlotRange->{0,3.45},PlotStyle->Thick]

s7[x_]=FourierSinSeries[x,x,7];

Plot[{s7[x],x},{x,0,Pi},PlotRange->{0,3.45},PlotStyle->Thick]

s8[x_]=FourierSinSeries[x,x,8];

Plot[{s8[x],x},{x,0,Pi},PlotRange->{0,3.45},PlotStyle->Thick]

Plot[{s1[x],x,s4[x],s8[x]},{x,0,Pi},PlotRange->{0,3.45},PlotStyle->Thick]