方向向量 + 法向量:把垂直、夹角、距离全变成解方程。
Consider our voting example from Section 1.2: three candidates A, B, and C are running for office. We decided that A …
甲和乙赢面一样大,丙只有他俩一半——然后甲退选了。按比例把甲的票重新分给乙和丙,答案干净得 2/3 和 1/3。