Selecting a Triangular region of a 2D data

Hi,

I have a 2D scatter plot. Now I want to select a triangular region in this plot and the use data inside the triangular region for further analysis.
Is there any way to do that?
How can I do that? Can anybody help?
I am very new in root.
Thanks in advance,
AK

How do you generate it ? it is it from a TTree simple create a TCutG with the triangle you need and draw your scatter plot using this cut.