(追記) (追記ここまで)
Area of a Convex Polygon
The coordinates (x1, y1), (x2, y2), (x3, y3), . . . , (xn, yn) of a convex polygon are arranged in the "determinant" below. The coordinates must be taken in counterclockwise order around the polygon, beginning and ending at the same point.
Find the area of this polygon:
See also