As shown in the figure, what is the area of the triangle with a (0,3), B (1,0) and C (2,2) as vertices

As shown in the figure, what is the area of the triangle with a (0,3), B (1,0) and C (2,2) as vertices

1. Make ABC three points in XY coordinate system. See the figure, the area of triangle = (2 + 3) * 2 / 2-3 * 1 / 2-2 * 1 / 2 = 2.5