Beta is the proportion of the area of the triangle represented by (Point, A, C). This triangle as well as the other triangles related to alpha and gamma have to make up the entire triangle, so the proportions of alpha, beta, and gamma have to add up to 1.

Beta is the proportion of the area of the triangle represented by (Point, A, C). This triangle as well as the other triangles related to alpha and gamma have to make up the entire triangle, so the proportions of alpha, beta, and gamma have to add up to 1.