Question: Extremepoints and increase/decrease intervals?

I am trying to get Maple 2021 to printout the intervals on which a differentiable function increases/decrease in a Maple document as part of a procedure. 

The function: 

A := x^2 + 400/x

the attempt. 

solve(evalf(diff(A, x) < 0))

which gives the result: RealRange(-infinity, Open(0.)), RealRange(Open(0.), Open(5.848035476))
There is no extreme point at x = 0 for A? So how do I get Maple to do an output which makes sense?  

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