Shape of functions

?curve
curve(1/(1+exp(-x)), from = -10, to = +10, n = 201, col = "blue")

curve(x*sin(x), from = 0, to = 50, n = 401, col = "red")

curve(sin(x), from = 0, to = 6*pi, col = "blue")
curve(cos(x), from = 0, to = 6*pi, col = "red", add = TRUE)