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发表于 17-1-2010 09:52 AM
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for第2题
let y=[e^(3x)](A+Bx)-------------(1)
dy/dx=[3e^(3x)](A+Bx)+Be^(3x)
=3y+Be^(3x)
hence, Be^(3x)=dy/dx-3y----------(2)
d^2y/dx^2=3(dy/dx)+3Be^(3x)
=3(dy/dx)+3[(dy/dx)-3y]
=6(dy/dx)-9y
hence, d^2y/dx^2-6(dy/dx)+9y=0
y=1 and dy/dx=0 when x=0
From(1), 1=1(A+Bx0) <=> A=1
From(2), Bx1=0-3x1 <=> B=-3
So, the particulation solution is y=[e^(3x)](1-3x)
看下是不是你要的。。。 |
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