hdu--2080 求角度

#include "stdio.h"#include "math.h"int main(){double x1,x2,y1,y2,recos,angle1,angle2,cos0,th;int n;scanf("%d/n",&n);while (n--){scanf("%lf %lf %lf %lf",&x1,&y1,&x2,&y2);angle1 = x1*x1+y1*y1+x2*x2+y2*y2-((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));angle2 = 2*sqrt((x1*x1+y1*y1)*(x2*x2+y2*y2));cos0 = angle1/angle2;th = acos(cos0);if(fabs(th) < 1e-5) th=(th>=0?0.00:180.00);else th = th/acos(-1)*180;printf("%.2f/n",th);}return 0;}