HDU 2080 夹角有多大II

#include <bits/stdc++.h>
using namespace std;

#define pi  3.14159265

int main() {
    int T;
    while(~scanf("%d", &T)) {
        for(int i =1 ; i <= T; i ++) {
            double x1, y1, x2, y2;
            scanf("%lf%lf%lf%lf", &x1, &y1, &x2, &y2);
            double l1, l2, l3, ans;
            l1 = sqrt(x1 * x1 + y1 * y1);
            l2 = sqrt(x2 * x2 + y2 * y2);
            l3 = sqrt((y2 - y1) * (y2 - y1) + (x2 - x1) * (x2 - x1));
            ans = acos((l1 * l1+ l2 * l2 - l3 * l3) / ( 2 * l1 * l2)) * 180 / pi;
            printf("%0.2lf\n", ans);
        }
    }
    return 0;
}