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问题: 微分方程问题14

解答:

z(t)=y(e^t)
==>
z'(t)=e^ty'(e^t)
==>
z''(t)=e^ty'(e^t)+e^(2t)y''(e^t)=
=z'(t)+e^(2t)y''(e^t).

==>
[z''(t)-z'(t)]+2z'(t)-2z(t)=e^t
==>
z''(t)+z'(t)-2z(t)=e^t
==>
z(t)=Ae^t+Be^(-2t)+te^t/3

==>
y(x)=Ax+B/x^2+xlnx/3