Extend Axes

Hi. I have a function I want to graph whose domain is only 0 to infinity, but I want the plot to show the negative x axis, too. How do I tell it to do this?

Right now I have:

using Plots  

x(u) = u
y(u) = sqrt(u)
y2(u) = -sqrt(u)
plot(x, [y, y2], 0, 5,
    framestyle = :origin,
    legend = :none,
    linecolor = :blue

xlim = [-1, 1]