由y=z'',z=y''得:y=y''‘’,特征方程为:r^4-1=0 r=±1和±i
解得:y=Ae^t+Be^(-t)+Csint+Dcost
y'=Ae^t-Be^(-t)+Ccost-Dsint
z=y'‘=Ae^t+Be^(-t)-Csint-Dcost
由y(0)=z(0)=0, y(π/2)=z(π/2)=1,代入得:
0=A+B+D; 0=A+B-D
1=Ae^(π/2)+Be^(-π/2)+C
1=Ae^(π/2)+Be^(-π/2)-C
解得:A=-1/(e^(-π/2)-e^(π/2)) B=1/(e^(-π/2)-e^(π/2)) C=0 D=0
y=(-e^t+e^(-t))/(e^(-π/2)-e^(π/2))
z=(-e^t+e^(-t))/(e^(-π/2)-e^(π/2))
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