求圆周率

public class test6 {


    public static void main(String[] args) {
        System.out.println("PI的标准："+Math.PI);
        double a=1;
        int n=6;
        for (int i = 0; i < 10; i++) {
            double b=Math.sqrt(0);
            b=Math.sqrt(1-(a/2)*(a/2));
            System.out.println(n+"边形 "+a*b/2*n);
            a=Math.sqrt(((a/2)*(a/2)+(1-b)*(1-b)));  //求次a
            n=n*2;
            //System.out.println(n+"边形 "+((a*Math.sqrt(1-(a/2)*(a/2)))/2)*n);
        }
    }

}