How to remove imaginary parts

ROOT
1

How to remove imaginary parts?
I am making function like following,

TF1 *f1 = new TF1(“f1”,"-10/sqrt(x) + 10", -10.0, 100.0);

I want to get just x>0 region function.
However, I had got x<0 also, like following.

dropbox.com/s/a73gw554hxje59o/fig.jpg?dl=0

How to get just x>0?
Please teach me!

2

TF1 *f1 = new TF1(“f1”,"-10/sqrt(x) + 10", 0.0, 100.0);

3

Dear couet,
Yes, thank you very much. It works for my analysis.

K