In[]:=
ClearAll["`*"];Remove["`*"];L=-Laplacian[u[x],{x}];s=DirichletCondition[u[x]==0,True];{vals,funcs}=DEigensystem[{L,s},u[x],{x,0,π},5]
Out[]=
{{1,4,9,16,25},{Sin[x],Sin[2x],Sin[3x],Sin[4x],Sin[5x]}}
In[]:=
Plot[Evaluate[funcs],{x,0,π}]
Out[]=
