Not exactly sure what you want to do. But you take the square root of negative numbers, which then is a complex number. I dont think you can give plot a complex number to plot? The following code works, maybe you can work your way from there...
```julia using Plots x=linspace(-2,2,100) f(x) = sqrt(complex(4.-x.^2)) g(x) = -sqrt(complex(4.-x.^2)) h(x) = sqrt(complex(-x.^2.+2*x)) k(x) = -sqrt(complex(-x.^2.-2*x)) plot(real(g(x)),x,aspect_ratio=1, show=true) readline() ``` On Monday, May 23, 2016 at 2:01:05 PM UTC-4, Henri Girard wrote: > > Always the same problem f and g works but h and after give this error. > I notice if I change x -4,4 I have got the same error > > Le 23/05/2016 19:02, Eric Forgy a écrit : > > Try x.^2. > > On Tuesday, May 24, 2016 at 12:48:49 AM UTC+8, Henri Girard wrote: >> >> Hi, >> I don't know why this plot doesn't work ? >> It tells me the domain is wrong ? >> I don't understand why ? >> Any help ? >> Regards >> Henri >> >> >> using Plots >> x=linspace(-2,2) >> f(x) = sqrt(4-x^2) >> g(x) = -sqrt(4-x^2) >> h(x) = sqrt(-x^2+2*x) >> k(x) = -sqrt(-x^2-2*x) >> plot([g,f,h,k],-2,2,aspect_ratio=1) >> > >
