Cross Product!

I'm calculating calculating the cross product of the angle formed by the first vertex and the last two vertices of a triangle. (The cross product here is counter clockwise and is negative; a point inside the triangle would alsways be negative, assuming it forms the 2nd leg. This is what I finally coded! 8-P)

Diamond at x: 64, y: 34
-1003, -93, -236

Cross Product: -1027.6, or 39.53 m. km^2
polygon(26.74% 37.86%, 55.27% 61.82%, 69.5% 27.1%)
The circumference is 49159.4 km and total area is 769.24 m. km^2, so the
area of the triangle is 114.2 m. km^2, 7.6% total