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Student Support Forum: 'DSolve and initial value problems' topicStudent Support Forum > General > Archives > "DSolve and initial value problems"

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Bill Simpson
10/19/12 12:15pm

I am guessing that some variable was set to some value after your first DSolve and before your second.

With a brand new fresh open notebook I try your example and get

In[1]:= DSolve[{y''[t]+4 y'[t]+4 y[t]==Sin[t],y[0]==0},y[t],t]

Out[1]= {{y[t] -> -(-4 - 25*t*C[2] + 4*E^(2*t)*Cos[t] - 3*E^(2*t)*Sin[t])/(25*E^(2*t))}}

In[2]:= Simplify[%]

Out[2]= {{y[t] -> (4/E^(2*t) + (25*t*C[2])/E^(2*t) - 4*Cos[t] + 3*Sin[t])/25}}

And then try your initial conditions and get

In[3]:= DSolve[{y''[t]+4 y'[t]+4 y[t]==Sin[t],y[0]==1,y'[0]==0},y[t],t]

Out[3]= {{y[t] -> -(-29 - 55*t + 4*E^(2*t)*Cos[t] - 3*E^(2*t)*Sin[t])/(25*E^(2*t))}}

In[4]:= Simplify[%]

Out[4]= {{y[t] -> (29/E^(2*t) + (55*t)/E^(2*t) - 4*Cos[t] + 3*Sin[t])/25}}

Try a fresh start and see if you can reproduce this.

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Subject (listing for 'DSolve and initial value problems')
Author Date Posted
DSolve and initial value problems Andrew R 10/18/12 11:32pm
Re: DSolve and initial value problems Bill Simpson 10/19/12 12:15pm
Re: DSolve and initial value problems Alex 10/19/12 12:16pm
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