void Calculate(Vector2 p1, Vector2 p2, Vector2 p3)
    {
        float a = Vector2.Distance(p2, p3);
        float b = Vector2.Distance(p1, p3);
        float c = Vector2.Distance(p1, p2);
        Debug.Log(a + "   " + b + "   " + c);


        float angleA = Mathf.Acos((b * b + c * c - a * a) / (2 * b * c)) * Mathf.Rad2Deg;
        float angleB = Mathf.Acos((a * a + c * c - b * b) / (2 * a * c)) * Mathf.Rad2Deg;
        float angleC = Mathf.Acos((a * a + b * b - c * c) / (2 * a * b)) * Mathf.Rad2Deg;

        Debug.Log(angleA + "   " + angleB + "   " + angleC);
    }

推到过程

已知 : A(1,0),B(4,6),C(−3,5) 三点

根据距离公式：d=

先算数三条边长 a b c

a=√(4+3)2+(6−5)2=√50

b=√(1+3)2+(0−5)2=√41

c=√(1−4)2+(0−6)2=√45

根据cos公式得到