This is incorrect. You are only using the chain rule for the part, so leave the sin(x) part out of it.
It should be:
Hi, everyone. First post but I have a feeling I'll be coming back often.
Problem: For what values of in the interval does the graph of have a horizontal tangent?
f(x) has horizontal tangents at
I don't have a problem getting the x-values for the horizontal tangents but I can't get the right derivative. Here's my work:
Substitute back into the equation.
Where is my error?
Thank you for your help,