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FP2 Differential equation question

I'm having issues with question 1, I get to what my working out shows, but -sinx does not differentiate to cosx. Where have I gone wrong?

Original post by Jabberjay_
I'm having issues with question 1, I get to what my working out shows, but -sinx does not differentiate to cosx. Where have I gone wrong?



Check your integrating factor. That's where you slipped up.
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Jabberjay_
OP
11
Original post by BuryMathsTutor
Check your integrating factor. That's where you slipped up.


Ah thanks, is the integrating factor just sin(1/x)?

EDIT: I mean, is it 1/sinx
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davros
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Original post by Jabberjay_
I'm having issues with question 1, I get to what my working out shows, but -sinx does not differentiate to cosx. Where have I gone wrong?



You've got a bit mixed up with your indices and logs!

Remember that −lnu=ln(1/u)-ln u = ln(1/u)
so

e−lnu=eln(1/u)=1/ue^{-ln u} = e^{ln(1/u)} = 1/u
Reply 4
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Jabberjay_
OP
11
Original post by davros
You've got a bit mixed up with your indices and logs!

Remember that −lnu=ln(1/u)-ln u = ln(1/u)
so

e−lnu=eln(1/u)=1/ue^{-ln u} = e^{ln(1/u)} = 1/u


Ah, thanks for the confirmation, I knew I was doing something wrong, as I had the same problem with the next question.
Original post by BuryMathsTutor
Check your integrating factor. That's where you slipped up.


Yeah the sin(x^-1) = -sinx is wrong I think.

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