For what values of x does the graph of f have a horizontal tangent? (Use n as your integer variable.)

Question

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)

=________

Answer 1

Wherever cos = -1/2, i.e. (2/3)π and (4/3)π and these 2 values plus integer multiples of 2π