Please help me with another deratives and tangent problem

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-2sin(x)

Answer 1

f(x) = x - 2sinx f'(x) = 1 -2cosx

Setting slope = f'(x) = 0, we obtain x = cos^-1(1/2) = π, 5π/6 (+ 2nπ for integral n)