# Math Help - absolute value/calculus

1. ## absolute value/calculus

Here is the question I'm having trouble with. Apparently the answer is A.

2. Originally Posted by scorpion007
Here is the question I'm having trouble with. Apparently the answer is A.

You need to find the derivative at $x=k$
But, the trick is that this an absolute value function.
The regular sine is negative in that interval
So you need to find the derivative of,
$y=-\sin x$
$y'=-\cos x$
At, k:
$-\cos k$

3. ah, thank you very much. That explains things.