You forgot the constant "2", derivative should be f'(x) = 1 + 2 cos x.
f has a horizontal tangent when f'(x) = 0.
Alright guys so I need someone to explain to me how to find the horizontal tangent for this question but in general I need to know it.
For what values of x does the graph of f have a horizontal tangent? (Use n as your integer variable. Enter your answers as a comma-separated list.)
f(x) = x+ 2 sin x
So I know the derivative is 1 + cosx I believe so what's the next step?