# Solving difficult integrals

1. Jul 17, 2011

### athrun200

1. The problem statement, all variables and given/known data
I have a problem in part b

2. Relevant equations

3. The attempt at a solution
How to integral the function?

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2. Jul 17, 2011

### athrun200

1. The problem statement, all variables and given/known data
I would like to ask for 18 and20

2. Relevant equations

3. The attempt at a solution
Again how to integral the function?

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3. Jul 17, 2011

### gb7nash

10a looks fine.

For 10b, take advantage of the following trig identity:

cosh2 x = [1 + cosh (2x)]/2

4. Jul 17, 2011

### athrun200

Oh no, I know this identity, but there are too many identity and formula so I can't remember it before you tell me. How can I make sure that I remember all of them? Or where can I check these useful identity?

5. Jul 17, 2011

### gb7nash

http://planetmath.org/encyclopedia/HyperbolicIdentities.html [Broken]

As far as knowing which ones to remember, it would depend on what you're trying to do and what class you're in. For a lot of integral problems, the identities I usually see are sin2 + cos2 = 1 (and any other pythagorean identities), and half/double angle formulas.

Last edited by a moderator: May 5, 2017
6. Jul 17, 2011

### athrun200

Thanks so much.
Shall we move on #2?
I just have some problems.

Last edited by a moderator: May 5, 2017