Mathematica rješenje

Clear[alfa, beta] ; l = π ; c = 1 ; alfa[x_] := 0 ; beta[x_] := 1/4 Sin[2 x] u = y[x, t] ... t u/.t0) beta[x], y[0, t] 0, y[l, t] 0}, y, {x, 0, l}, {t, 0, 8}]

RowBox[{{, RowBox[{{, RowBox[{y, , TagBox[RowBox[{InterpolatingFunction, [, RowBox[{Ro ... Box[{{, RowBox[{0., ,, 8.}], }}]}], }}], ,, <>}], ]}], False, Editable -> False]}], }}], }}]

Plot3D[Evaluate[y[x, t] /. First[rjes]],
   {x, 0, l}, {t, 0, 8}, PlotPoints->30]

[Graphics:../HTMLFiles/zicavalnajed_223.gif]

⁃SurfaceGraphics⁃

<<Graphics`Animation`

RowBox[{RowBox[{Animate, [, RowBox[{Plot[Evaluate[y[x, t]/.First[rjes]], {x, 0, l}, PlotRange {-1, 1}], ,, RowBox[{{, RowBox[{t, ,, 0, ,, 8, ,, 0.2}], }}]}], ]}], ;}]

[Graphics:../HTMLFiles/zicavalnajed_267.gif]

Created by Mathematica  (December 3, 2003)