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#1 2012-06-03 22:36:53
- amberzak
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- Registered: 2012-03-16
- Posts: 80
Harder Substitution
By using the Substitution u=cot theta or otherwise, find the integral of cot ^4 theta d theta
My teacher says there is a really simple way to do this, so it shouldn't take hours.
He also gave us a hint of writing down sec^3 theta and tan theta, but I can't see how we can get to that.
Any ideas?
Don't think outside the box. Think there is no box
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#2 2012-06-04 05:01:36
- anonimnystefy
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- From: Harlan's World
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Re: Harder Substitution
Hi amberzak
Have you tried the substitution t=tan(theta)?
Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.
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#3 2012-06-04 05:06:47
- Bob
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Re: Harder Substitution
hi amberzak,
Bob
ps. I don't get the hint. Threw it away and did without.
Children are not defined by school ...........The Fonz
You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you! …………….Bob 
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#4 2012-06-04 05:17:35
- amberzak
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Re: Harder Substitution
Anon, I have not yet. How would I do that?
Bob, I am guessing it's still answer in process. I get so far and then couldn't get further. I think the sec^3 theta tan theta is a hint.
Don't think outside the box. Think there is no box
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#5 2012-06-04 05:22:15
- Bob
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Re: Harder Substitution
hi amberzak,
I couldn't make any sense of the hint. My post above is complete. I've just got to check by differentiation.
Bob
Children are not defined by school ...........The Fonz
You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you! …………….Bob
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#6 2012-06-04 05:24:32
- Bob
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Re: Harder Substitution
Yes, that works! :):)
Bob
Children are not defined by school ...........The Fonz
You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you! …………….Bob
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#7 2012-06-04 05:30:02
- anonimnystefy
- Real Member
- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,049
Re: Harder Substitution
Hi Bob
Yes, that works!
Bob
I still can't understand the hint.
Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.
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#8 2012-06-04 05:43:58
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Harder Substitution
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
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#9 2012-06-04 05:49:14
- anonimnystefy
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- From: Harlan's World
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Re: Harder Substitution
Her voice is so thin compared to Chris Martin's.I cannot listen to Viva la Vida while listening to her.
Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.
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#10 2012-06-04 05:52:55
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Harder Substitution
Maybe, but Amber may like to see it.
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
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#11 2012-06-04 05:54:35
- anonimnystefy
- Real Member
- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,049
Re: Harder Substitution
Who is Amber and what does she want to see?
EDIT:Oh,you meant amberzak! You never call people on this forum by their real names,even if you know them (with the sole exception of Bob).
Last edited by anonimnystefy (2012-06-04 05:55:36)
Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.
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#12 2012-06-04 06:25:29
- Bob
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Re: Harder Substitution
hi Stefy,
I still can't understand the hint.
Me neither.
Is it compulsory to follow a hint?
Bob
Children are not defined by school ...........The Fonz
You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you! …………….Bob
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#13 2012-06-04 06:26:34
- anonimnystefy
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- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,049
Re: Harder Substitution
Yes, that works!
Bob
What was this then?
Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.
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#14 2012-06-04 07:01:04
- Bob
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Re: Harder Substitution
That was me being triumphant, because I had tested my integration and it works (ie. when you differentiate it, you get cot^4 theta.)
Please look at post #3
Bob
Children are not defined by school ...........The Fonz
You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you! …………….Bob
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#15 2012-06-04 07:04:22
- anonimnystefy
- Real Member
- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,049
Re: Harder Substitution
Yes,I have seen your method. Why did you think it would work? And don't you think I would have immediately told you if there was something wrong with your working?
I have sent you an e-mail.
Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.
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#16 2012-06-04 07:32:21
- amberzak
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- Registered: 2012-03-16
- Posts: 80
Re: Harder Substitution
It's okay, my real name isn't amberzak.
What was the method you used bob? And thanks, you have been very helpful
The link you gave me doesn't work 
Last edited by amberzak (2012-06-04 07:35:58)
Don't think outside the box. Think there is no box
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#17 2012-06-04 07:40:33
- Bob
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Re: Harder Substitution
See post #3
Bob
Children are not defined by school ...........The Fonz
You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you! …………….Bob
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#18 2012-06-04 08:55:56
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Harder Substitution
Hi amberzak;
The link you gave me doesn't work
Did you mean my link? It is working fine here.
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
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#19 2012-06-08 23:14:06
- amberzak
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- Registered: 2012-03-16
- Posts: 80
Re: Harder Substitution
It's working today 
Don't think outside the box. Think there is no box
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#20 2012-06-08 23:29:54
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Harder Substitution
Hi amberzak;
Very good! The video is Bob's method so you can use it to strengthen your understanding of what he did.
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
Offline
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