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# Integration by Parts watch

1. Hopefully somebody will be able to help me with this.
For some reason I am ending up with 0=0 for an answer, I think it may be me getting signs mixed up somewhere.
Here is my question and workings out:-

Where am I going wrong?

Barney
2. you have to stick to using the same functions for u and dv/dx, otherwise...

(i.e. for the 2nd integration, stick with u=exp term, dv/dx = trig term)
3. For the second by parts let again and

Keep the u and dv/dx the same parts.
4. So using:-

I get:-

Where do I get the for the substitution of I?

Barney
5. if the,

giving the last part as

then - because you have a multiple of the same integral on the LHS (muliply both sides by 4 and youll see this), you can put the same one all on one side of the equals sign and...
6. I thought you only did the derivative of u, and that you integrated .

Barney
7. But, i was pointing out that, when you integrated your dv/dx you got Sin(x)Cos(x), when in fact the answers (1/2)Sin(2x).

Hang on.. ill type out what you should get (but not the answer, cause thats the easy part - youve basically got it, but i think the arithmetic is maybe freaking you out!)

8. taking the second part:

giving, together:

multiply this by 4, and take the last term over to the LHS...
9. Sorry for the delay and also potentially being thick, but where did the come from?

Barney
10. !!!!Bump!!!!
11. (Original post by Barney63)
Sorry for the delay and also potentially being thick, but where did the come from?

Barney
From
12. maybe this will explain it better...

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