# Thread: I don't understand how this is true? (derivatives)

1. ## I don't understand how this is true? (derivatives)

How is the answer in part a the derivative of the given function? Here's the problem:
ImageShack&#174; Math problem help

I get: s'(t) = A(-sin(wt+d)) x d/dx (wt+d)

but isnt the derivative of (wt+d), when w and d are constants, 0?

2. $\frac{d}{dt}(wt+d)= w$

3. nevermind. I got it now. Thanks !