[Erel]

Works fine here (don't forget to create a form named Form1).

Sub Globals
    'Declare the global variables here.
    Dim x(3),y(3)
End Sub

Sub App_Start
    x(0)=0 :y(0)=0 :x(1)=0: y(1)=100: x(2)=200: y(2)=100
    form1.polygon(x(),0,y(),0,3,cRed)
    Form1.Show
End Sub

I prefer to use a structure:

Sub Globals
    'Declare the global variables here.
    Dim Type(x,y) points(3)
End Sub

Sub App_Start
    points(0).x = 0
    points(0).y = 0
    points(1).x = 0
    points(1).y = 100
    points(2).x = 200
    points(2).y = 100
    form1.polygon(points(),0,3,cBlue)
    Form1.Show
End Sub