I'm not sure why im getting a complex solution for evalf(h(-1/2)). Posted screenshot here:

http://prntscr.com/8abmta

The answer should be positive 6*2^(2/3) ≈ 9.52

 The computer returns

h(-1/2) =

=

The problem is that evalf((-1)^(1/3)) you get 0.500 + .866I

Is there no way to evaluate a second derivative of a real valued function which has a fractional exponent without receiving complex results? I don't have the time to look at each function and try to figure out what went wrong. I want to plug in any x value into a function defined for all reals and get a real result.

I tried  assume(x , 'real' ) , that did not do anything.

WHen I type:

I get nothing, a blank box. But if I change the code slightly, by squaring both sides, then it works.

What is the reason for this. I uploaded an image of the output:  http://prntscr.com/752mtd