Heron's formula w/points from polygon

Here's my problem: After given vertices of a n-sided polygon(x,y), I need to use Heron's formula to find the area of the n-2 triangles it creates. My problem is I cannot figure out how to say I want to pick out triangles 123 134 145 and so on. I need to make a function for Heron's formula and while I know how to find the distances from the lines, I cannot figure out how to specify which points to use. Any help would be appreciated.

Answer 1

[bym]

How about:

combnk(1:5,3)

[Lukas Setiawan]

Here the solution with gui where the heron's function write by Marco zuliani bitbucket.org/nixz97/nix/downloads/