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IMPORTANT: You must wait until midnight (morning exams)/4.30AM (afternoon exams) to discuss Edexcel exams and until 1pm/6pm the following day for STEP and IB exams. Please read before posting, including for rules for practical and oral exams. 28-04-2013
1. Integration by substitution
Turns out I'm finding integration by substitution the most challenging part of the whole A-level. I'm not sure if its meant to be; I'm probably missing something.

But I really cannot solve this at all:

using .

The answer is supposed to be:

So here's what I do:

Then the integral becomes:

which to me seems unsolvable. So I must have done something wrong but I can't imagine how I could do it differently. I've tried about ten times, so could someone please help me. I would really appreciate it.
Last edited by JeremyB; 28-05-2012 at 19:42.
2. Re: Integration by substitution
3. Re: Integration by substitution
(Original post by JeremyB)

Then the integral becomes:

I didn't check you whole post but

The second term is a standard inegral.
4. Re: Integration by substitution
(Original post by ecraven)
Oops yes that's what I got but I copied it wrong on the computer.
5. Re: Integration by substitution
(Original post by JeremyB)
Turns out I'm finding integration by substitution the most challenging part of the whole A-level. I'm not sure if its meant to be; I'm probably missing something.

But I really cannot solve this at all:

using .

The answer is supposed to be:

So here's what I do:

Then the integral becomes:

which to me seems unsolvable. So I must have done something wrong but I can't imagine how I could do it differently. I've tried about ten times, so could someone please help me. I would really appreciate it.

Use partial fraction on
6. Re: Integration by substitution
(Original post by BabyMaths)
I didn't check you whole post but

The second term is a standard inegral.
Thanks a lot for that. Simple enough once you see it.
7. Re: Integration by substitution
(Original post by BabyMaths)
I didn't check you whole post but

The second term is a standard inegral.
As the OP is struggling on integration by substitution(C4 topic), so i am quite sure that he doesn't knows the standard integral you are talking about. He is probably working at C4 not FP3, this integral is in FP3.

Actually he has probably made a sign error.
8. Re: Integration by substitution
(Original post by raheem94)

Use partial fraction on
Thanks mate. I can see it now.
9. Re: Integration by substitution
(Original post by JeremyB)
Thanks a lot for that. Simple enough once you see it.
Do you really know how to integrate

I thought you are working at C4
10. Re: Integration by substitution
(Original post by raheem94)
Do you really know how to integrate

I thought you are working at C4
Yeah I wrote that one wrong on the computer when I was copying it from my notes.

What I've been getting is u^2 / (u^2 - 4), which as you said I would do with partial fractions once simplified. My problem was the algebra involved in simplifying it first.

Have you got any tips for solving these integration by substituion problems? I don't know why I'm finding it so tricky.
Last edited by JeremyB; 28-05-2012 at 20:25.
11. Re: Integration by substitution
(Original post by JeremyB)
Yeah I wrote that one wrong on the computer when I was copying it from my notes.

What I've been getting is u^2 / (u^2 - 4), which as you said I would do with partial fractions once simplified. My problem was the algebra involved in simplifying it first.

Have you got any tips for solving these integration by substituion problems? I don't know why I'm finding it so tricky.
I don't have many tips for it, just practice more, with practice you will become better at recognizing the next steps.

At first it looks difficult, but soon, with more practice, it becomes very easy.
12. Re: Integration by substitution
(Original post by raheem94)
As the OP is struggling on integration by substitution(C4 topic), so i am quite sure that he doesn't knows the standard integral you are talking about. He is probably working at C4 not FP3, this integral is in FP3.

Actually he has probably made a sign error.
I believe you are correct.

Sorry.
13. Re: Integration by substitution
(Original post by BabyMaths)
I believe you are correct.

Sorry.
No problem.