How do you simplify: (x^(3/2))(x+x^(5/2)-x^2)

factor out an x:

x^(5/2) (1 + x^(3/2) - x)

can't do much with that. Even letting v = x^(1/2) to get

v^5 (v^3 - v^2 + 1)

I don't see where you can really factor anything else out