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 ofxdoes the graph offhave a horizontal tangent? (Usen as your integer variable. Enter your answers as a comma-separated list.)

f(x) =x+ 2 sinx

So I know the derivative is 1 + cosx I believe so what's the next step?