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# C4 Integration by Substitution watch

1. Hiya

I was just doing q2 and has just gotten to the part where I subbed in the values to get it all in terms of u, but disaster struck when du was wildly in the middle of the equation.

So, my question is is it the same as having du at the end of the equation as it is multiplied or have I just gotten in to a complete mess?

Also: I have just realised that there should be brackets around the
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Thanks!
2. (Original post by KaylaB)
Hiya

I was just doing q2 and has just gotten to the part where I subbed in the values to get it all in terms of u, but disaster struck when du was wildly in the middle of the equation.

So, my question is is it the same as having du at the end of the equation as it is multiplied or have I just gotten in to a complete mess?

Also: I have just realised that there should be brackets around the
Spoiler:
Show
Thanks!
Yes, I think you're fine, you can just move the du over to the end if you wish (don't forget the -!)
3. (Original post by SeanFM)
Yes, I think you're fine, you can just move the du over to the end if you wish (don't forget the -!)
So is this right?
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The du being multiplied by a certain part is stressing me out
4. (Original post by KaylaB)
So is this right?
Spoiler:
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The du being multiplied by a certain part is stressing me out
Should be fine, just don't forget that e^u is being multiplied by (e-e^2), you may make a mistake as your brackets aren't always there.
5. (Original post by KaylaB)
So is this right?
Spoiler:
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The du being multiplied by a certain part is stressing me out
I think there is an equal missing in the printed question.
6. Ok so Ive dont it and all I belive there is a misprint in the question they forgot the = signt after the dx so actually du is not in a middle of an equation there is an equal sign after the du so you need show how when u integrate you will get e(e-1).

So techniclly you will inegrate -eu which is the same -eu that is the same as -ecos(X)+1 it will eventually give you the same answer just try it out. hope that is what u were asking?
7. (Original post by SeanFM)
Should be fine, just don't forget that e^u is being multiplied by (e-e^2), you may make a mistake as your brackets aren't always there.
(Original post by M14B)
I think there is an equal missing in the printed question.
(Original post by koolgurl14)
Ok so Ive dont it and all I belive there is a misprint in the question they forgot the = signt after the dx so actually du is not in a middle of an equation there is an equal sign after the du so you need show how when u integrate you will get e(e-1).

So techniclly you will inegrate -eu which is the same -eu that is the same as -ecos(X)+1 it will eventually give you the same answer just try it out. hope that is what u were asking?
Ah okay after a few minutes googling this question. It turns out this question was printed like this, but you're right, there's supposed to be an equals sign between dx and e(e-1)

Thank you all for your help!

I shall be notifying my teacher and complaining that she failed to check the homework
8. what was I thinking..

well done anonwinner
9. (Original post by SeanFM)
x
Okay sorry but same (corrected) question, new problem. I now have this with the negative respect to u, would I just multiply everything by -1/take it out as a factor?

Also, this is just a proving question right? so showing that the first part is the same as e(e-1) or would I need to integrate it as well?
10. (Original post by KaylaB)
Okay sorry but same (corrected) question, new problem. I now have this with the negative respect to u, would I just multiply everything by -1/take it out as a factor?

Also, this is just a proving question right? so showing that the first part is the same as e(e-1) or would I need to integrate it as well?
It's just -1 * du so you can move the -1 outside the integral if you want as it is a constant.

11. i tried this q but got up to e^u(e^2-e) is this q wrong? i cant get further

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12. (Original post by SeanFM)
It's just -1 * du so you can move the -1 outside the integral if you want as it is a constant.

Ah okay, solved! I've finally cracked this question!

Thanks so much for your help
13. (Original post by ranz)
i tried this q but got up to e^u(e^2-e) is this q wrong? i cant get further

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The question is wrong, it seems. There should be an = sign after the dx.

(Original post by KaylaB)
Ah okay, solved! I've finally cracked this question!

Thanks so much for your help
14. wait i tried it again and u just dont integrate(e^2-e) i got 21.8 as the answer

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15. (Original post by ranz)
wait i tried it again and u just dont integrate(e^2-e) i got 21.8 as the answer

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You don't integrate the e(e-1) part, you're just proving that the first part can be written as that in the end
16. (Original post by KaylaB)
You don't integrate the e(e-1) part, you're just proving that the first part can be written as that in the end
oh isnt this a solve q?

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17. (Original post by ranz)
oh isnt this a solve q?

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Nah, that's what I thought at the start too
18. (Original post by KaylaB)
Nah, that's what I thought at the start too
i tried proving it but i just ended up with e^cosx+1/sinx + x not e(e-1) im probably doing something wrong

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19. (Original post by ranz)
i tried proving it but i just ended up with e^cosx+1/sinx + x not e(e-1) im probably doing something wrong

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It wants you to do it all in terms of u. So this is how I did it
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20. ohhh i see, thankkks! i get it now 😊😊

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