1636.sagews

f(x) = cos(x) - cos(x - 2*pi/3)
p1 = plot(cos(x), 0, 20, rgbcolor='red')
p2 = plot(cos(x - 2*pi/3), 0, 20, rgbcolor='blue')
p3 = plot(f, 0, 20, rgbcolor='green')
show(p1 + p2 + p3)