using an app command in cas. (area)

[parisse]

area (lowercase) is a CAS command used for geometry, it handles geometric objects (area(circle(0,1)) or area(1,2,i) for a polygon with vertices of affixes 1, 2 and i). It will also returns the area under a curve if you provide the following arguments: expression, variable=lower..upper like area(sin(x),x=1..2).
In your example, your arguments are interpreted as affixes of 3 vertices of a triangle, all on the x axis, therefore the polygon has area 0.