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# Differentiation question watch

1. Right I have to differentiate the following:

It seems so simple to me, but it's got me stumped, I can't remember if I treat it as a compound function, the product rule and set u = cos v, or to do the chain rule.

all help appreciated.
2. chain rule
3. Chain rule
4. so if my head is on straight I should get:

as the two minuses from -sin and should cancel out?
5. (Original post by BillV3)
Right I have to differentiate the following:

It seems so simple to me, but it's got me stumped, I can't remember if I treat it as a compound function, the product rule and set u = cos v, or to do the chain rule.

all help appreciated.

The bit in the bracket after cos (inside function ) stays the same. Using the chain rule, you multiply by the derivitive by the derivitive of the inside function.
6. ye I got that in the end, had a sudden 'hang on a minute its just ........' moment, I'll just blame it on a mind blank, they seem to be happening with alarming frequency these days
7. (Original post by BillV3)
ye I got that in the end, had a sudden 'hang on a minute its just ........' moment, I'll just blame it on a mind blank, they seem to be happening with alarming frequency these days
Lol!

This may make it a bit easier :

Let u =
Then

So the first equation can be written as :

Now using the chain rule :

8. ah your final answer seems to match mine, I just didn't have the steps in between, I think my brains trying to tell me it needs a rest when I start trying to do the product rule on that lol.

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Updated: November 11, 2008
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