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# Help on a DE watch

1. Hi, I'm having trouble seeing how the solution to the following:

comes to . (C is an arb. const.)

I would usually have used separation of variables, but it doesn't seem to work here.

Thanks.

EDIT: ok, i've got the result, except for the modulus signs...why do they need to be applied? Is it because the natural log is undefined for negative arguments?
2. Why does it not work? That is a separable equation...

don't forget the minus sign though, and what that does to any logarithms.
3. (Original post by em12)
Hi, I'm having trouble seeing how the solution to the following:

comes to . (C is an arb. const.)

I would usually have used separation of variables, but it doesn't seem to work here.

Thanks.

EDIT: ok, i've got the result, except for the modulus signs...why do they need to be applied? Is it because the natural log is undefined for negative arguments?
ermmm

Therefore, is what i get, but i dont know how to write like this and its on internet not paper :P
4. (Original post by em12)
EDIT: ok, i've got the result, except for the modulus signs...why do they need to be applied? Is it because the natural log is undefined for negative arguments?
Well i do know that if you integrate or you get or , if that helps. Sorry i've never done DE but i know differential equations from C4
5. (Original post by em12)
Hi, I'm having trouble seeing how the solution to the following:

comes to . (C is an arb. const.)

I would usually have used separation of variables, but it doesn't seem to work here.

Thanks.

EDIT: ok, i've got the result, except for the modulus signs...why do they need to be applied? Is it because the natural log is undefined for negative arguments?
I hope this is correct.

6. (Original post by Small123)
ermmm

Therefore,
(let e^c = k)

so (where k is an arbitrary constant)
Thanks steve2005 i can see the error in my solution i should have divided the LHS by y not timesed it. so ill amend my post.
7. (Original post by Small123)
ermmm

Therefore,
(let e^c = k)

so (where k is an arbitrary constant)
Also do you have to consider the solution of when ,
So the solutions become, and where C is an arbitrary constant?

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