solving sqrt(-1) to a real number

edit

Here is what I am trying to do:

var('x')
A(x)=x/2+(4-x*x)^(1/2)
assume(0<x<2)
maximum = (derivative(A)==0).maxima_methods().rootscontract().simplify()
view(maximum)
view(solve(maximum,x))
A.plot(A,0,2)

and get i multiplied by the root of x^2... if I put the same equation into wolfram, it gives me a real number 2/sqrt(5) (which is correct and makes sense).

How can I make SageMath solve those? I tried simplify() and full_simplify(), maxima_methods() and rootscontract() gives an error in combination with solve().

I guess it's just some syntax error, sorry for that :(

For now I do most in the Sage - Cell Server, which is great.