此题知道反三角函数的反余弦函数即可
import java.util.Scanner;
public class Main{
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int n = sc.nextInt();
while(n-->0){
double x1 = sc.nextDouble();
double y1 = sc.nextDouble();
double x2 = sc.nextDouble();
double y2 = sc.nextDouble();
double a = x1*x1+y1*y1;
double b = x2*x2+y2*y2;
double c = (x1-x2)*(x1-x2)+(y1-y2)*(y1-y2);
double d = ( Math.acos(((a+b-c)/(2*Math.sqrt(b)*Math.sqrt(a)))))*180/Math.PI;
System.out.printf("%.2f",d);
System.out.println();
}
}
}