# Strange differentiation

1. May 6, 2007

### malawi_glenn

This is a problem and i show you my work, what i dont understad is how to differentiate things like:

d(cos(t)) / dp

is all i have done so far madness? or where iam i doing wrong?

(i did not got the answer myself)

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2. May 6, 2007

### cristo

Staff Emeritus
I can't see your attachment (it's not been approved yet) but to perform that derivative, you use the chain rule. So
$$\frac{d}{dp}(\cos t)=-\sin t\frac{dt}{dp}$$

3. May 6, 2007

### HallsofIvy

Staff Emeritus
In the attachment, you are also given that p= A/2 sin t so that t= arcsin(2p/A)

You calculation looks correct except that you have forgotten the "-": d(cos(t))/dt= - sin(t) so -sin(arcsin(2p/A)= -2p/A.

4. May 6, 2007

### lalbatros

HallsofIvy,

It is a bit frustating that you had the possibility to read the attachement and give a comment on it, while other members have not yet been able to read it because it is "pending".

Last edited: May 7, 2007