The trick to removing the horizontal line is to make the calculator think the left side (or whatever portion) of the graph is imaginary and thus can't be displayed. To remove the left side, for example, multiply the equation by $\sqrt{X}/\sqrt{X}$; this is simply equal to 1, but the calculator thinks it's imaginary for the left side (since the square root of a negative number is imaginary). So, for your graph, type in $X^2(\sqrt{X}/\sqrt{X})$. If you wanted to remove the right side instead, replace the factor by $\sqrt{-X}/\sqrt{-X}$, and in general you can adjust the bounds by changing what's under the square root to make the parts you don't want completely imaginary. The one downside to this method is that the calculator doesn't like $\sqrt{0}/\sqrt{0}$, so instead of graphing for all X≥0 it is only X>0; the difference is barely noticeable on the graph itself.

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