hdu1724数学题，定积分求面积，保留三位小数

定积分求面积，求起来应该不难，但公式应该很复杂，懒得求了，直接套公式了。

import java.text.DecimalFormat;
import java.util.Scanner;

public class hdu1724 {
    public static void main(String[] args) {
        double PI = 3.14159265;
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        for (int i = 0; i < n; i++) {
            int a = sc.nextInt();
            int b = sc.nextInt();
            int l = sc.nextInt();
            int r = sc.nextInt();
            if (l==r){
                System.out.println("0.000");
            }else{
                double sita1 = -Math.acos(1.0*l/a);
                double sita2 = -Math.acos(1.0*r/a);
                double s1=Math.abs(1.0/2*a*b*(PI-sita1))+1.0*a*b/4*(Math.sin(2*sita1));
                double s2=Math.abs(1.0/2*a*b*(PI-sita2))+1.0*a*b/4*(Math.sin(2*sita2));
                String format = new DecimalFormat("#.000").format(Math.abs(2*(s2-s1)));
                System.out.println(format);
            }
        }
    }
}