求向量夹角

向量夹角公式：

cosα = AB / (|A||B|)

设A(x1,y1),B(x2,y2);

cosα =(x1x2 + y1y2) / sqrt( (x1^2 + y1^2) * (x2^2 + y2^2) )

代码实现(c++)：

#include <math.h> //Calcucate angle between vector A and B//返回角度; return degreeint CalculateVectorAngle(int x1, int y1, int x2, int y2){    //acos return radian,we should transform it into degree    return acos((x1*x2 + y1*y2) / sqrt((x1*x1 + y1*y1)*(x2*x2 + y2*y2)) * 180 / 3.14;}

原文链接: https://www.cnblogs.com/little-ant/archive/2011/05/27/2060377.html

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