Should be a simple diff eq but my answer is different than the books

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Homework Help Overview

The discussion revolves around a first-order differential equation given by dy/dt = 3 + e^(-t) - 1/2*y. The original poster expresses confusion regarding their solution compared to the solution provided in a textbook.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants are exploring the original poster's solution and questioning the steps taken to arrive at that solution. There are requests for the original work to verify the calculations and reasoning.

Discussion Status

Some participants have pointed out potential errors in the original poster's calculations and have encouraged them to show their work for better clarity. There is an ongoing examination of the steps involved in solving the differential equation, with hints at missing factors and the importance of constants in the solution.

Contextual Notes

The original poster mentions having worked on the problem multiple times, indicating a struggle with the solution process. There is also a note about the difficulty in typing out the work, which may affect the clarity of the discussion.

myusernameis
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Homework Statement


dy/dt = 3+e^(-t) - 1/2*y

Homework Equations



The Attempt at a Solution



how come i got y = 6e^(1/2t) + 2e^-t - 3

when the book has y = 6-2e^(-t) - 3e^(-t/2)
 
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Since you didn't show your work, it's a bit tough to know how you arrived at your answer. Show your work, please.

It is rather easy to verify that your result is incorrect and that the book's is correct. Your result does not satisfy the given differential equation; the book's does. It is a good idea to always double check your work.
 
D H said:
Since you didn't show your work, it's a bit tough to know how you arrived at your answer. Show your work, please.

It is rather easy to verify that your result is incorrect and that the book's is correct. Your result does not satisfy the given differential equation; the book's does. It is a good idea to always double check your work.


ok, it's just that it takes me a long time to type all the work, and I've done this problem for > 3 times now

ok, i'll type up my work haha

thanks
 
[itex]1/2y + dy/dt = 3 + e^{-t}[/itex]

[itex]e^{1t/2}y = 3 (integral)(e^{(1t/2)} + e^{-t}*e^{(1t/2)}[/itex]

[itex]y = 6e^{(1t/2)}-2e^{(-1t/2)}[/itex]

that's only the general solution, since i need to get this right in order to figure out the particular solution...
it's actually (1/2)t, not 1/(2t)..
 
Step 2 does not follow from step 3. You dropped a key factor.
 
D H said:
Step 2 does not follow from step 3. You dropped a key factor.

O LOLzzz

did i forget about c?

hahaha ...
 
No, you did not forget about c. (Well, you did, but that is not what I was talking about.)

Look at the left-hand side of your second equation.
 
D H said:
No, you did not forget about c. (Well, you did, but that is not what I was talking about.)

Look at the left-hand side of your second equation.


haha alright, thanks i think i got it
 

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