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# help please-integration by subs watch

1. could someone give me a step-by-step solution to:

integrate cos(x).sin(x)^7.dx

thanks
2. u = sin(x)
du = cos(x) dx

integrate u^7 du
=(u^8)/8 + c
=sin(x)^8 + c

I think, no doubts people will correct me if i'm wrong
3. Sinx^8 divided by 8- i think thats right never understood it mind but its just a rule!
4. use substitution method.
u = sin(x)
du = cos(x)

dx= integral u^7 du
= (u^8)/8+c

Substitute back for u = sin(x)therfore you get = (sin^8(x))/8+c

5. This is an example of the

6. generally the idea is to give hints as how to get to the answer on here, just giving the OP the answer isn't going to be that helpful for them in the long run.
7. (Original post by 2^1/2)
generally the idea is to give hints as how to get to the answer on here, just giving the OP the answer isn't going to be that helpful for them in the long run.
hate to cause an argument but in my experience if the person cares enough to post it on the net, they are going to try and understand where the answer came from. A full method is far more useful than bits of advise from loads of people, which is just confusing.
8. thanks everyone for the help i understand it now
9. (Original post by Will1692)
hate to cause an argument but in my experience if the person cares enough to post it on the net, they are going to try and understand where the answer came from. A full method is far more useful than bits of advise from loads of people, which is just confusing.
not my rules - but i agree with them (full solutions are ok if you start to confuse the OP and as a last resort not the first thing), read the sticky at the top of the maths section

The key aim here is to show the original poster how they can answer the question. There is actually quite a lot of skill and experience involved in doing this well. For example, if they are stuck using a particular method, the ideal is to show them how to get that method to work, not to show them a solution using a completely different technique.

In general, the best approach is to give small 'nudges' in the right direction; in contrast, posting full solutions is frowned upon.

Try to remember that people posting here have widely differing experience levels and educational backgrounds. Just because someone has posted what you consider an extremely simple question, it doesn't give you any right to try to make them feel inferior about it.

By the same token, please try to use common sense when deciding if you can answer a question. If a thread has 15 detailed posts from people at university level with no resolution, it is somewhat unlikely someone studying AS maths will be able to help. That doesn't mean you can't try, but do take the time to read the other posts and check you really understand what's going on before posting anything.

On Posting Full Solutions

This is a thorny topic, which has probably caused more arguments than anything else on this forum. To make it perfectly clear, the consensus (and forum rule), is that posting of full solutions should be considered a last resort. If your first contribution to a thread is to post a full solution, the moderators are quite entitled to take action (though discretion can be used).

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Updated: January 18, 2010
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