How is it going guys? I have a test next week and there are a couple of questions on my test review that I don't understand. Here they are:

1. For what values of x does the graph f have a horizontal tangent.

a. f(x)= x + 2cosx b. f(x)= (e^x) (sinx)

- Regarding these problems, I know how to find the derivative, but have no idea what to do next to solve it.

2. Let f(x)=x-2cosx, where x is greater than or equal to 0, but less than or equal to 2 pie.

a. On what intervals is f increasing or decreasing?

b. On what intervals is f concave upward or concave downward?

3. Find equations of both lines that are tangent to the curve y=1+x^3 and parallel to the line 12x-y=1.

Help or any feedback would be greatly appreciated, thanks.