问使用java的maclaurin级数arccos计算出了什么问题？

EN

    public class Maclaurin {

    public static int factorial(int fact) {
        if(fact==0)
            return 1;
        return fact*factorial(fact-1);
    }

    public static void main(String[] args) {
    int i, j;
    double function = 0, x,result;

    x=0;

        for (int n = 0; n < 8; n++) {

            function=((factorial(2*n))/(Math.pow(4, n)*Math.pow(factorial(n),2)*(2*n+1)))*Math.pow((Math.pow(x, 2)-1),2*n+1);
            result=(Math.PI/2)-function;

            System.out.println("x= "+x+" y= "+result);
            System.out.println("Test "+Math.acos(Math.pow(x, 2)-1));
            x+=0.13;
        }




    }


    }

Programm output. test is a value calculated with Math.arccos and it differs from y calculated with mclaurins formula:

    x= 0.0 y= 2.5707963267948966
    Test 3.141592653589793
    x= 0.13 y= 1.7291549939933966
    Test 2.9574849820283498
    x= 0.26 y= 1.6236496851024964
    Test 2.771793621843802
    x= 0.39 y= 1.5848621264898726
    Test 2.5828078861333155
    x= 0.52 y= 1.5725761587226181
    Test 2.3885331918392687
    x= 0.65 y= 1.5708496332463704
    Test 2.1864594293995867
    x= 0.78 y= 1.570796415168701
    Test 1.9731661516473589
    x= 0.91 y= 1.5707963267948972
    Test 1.7435543826662978

public class Maclaurin {
    private static double x;

//public static int factorial(int fact) {
//    if(fact==0)
//        return 1;
//    return fact*factorial(fact-1);
//}
   public static double factorial(int fact) {
    if(fact==0)
        return 1;
    return fact*factorial(fact-1);
}

public static void main(String[] args)
    {
         x = 0;
        for (int i=0;i<8;i++)
            {
                maclaurin(x);
                x=x+0.14;
            }

    }

public static void maclaurin(double value){
    double function = 0, x, result;

    x =value;

    for (int n = 0; n < 20; n++) {
        function += ((factorial(2 * n)) / (Math.pow(4, n) * Math.pow(factorial(n), 2) * (2 * n + 1)))
                * Math.pow((Math.pow(x, 2) - 1), 2 * n + 1);
    }

    result = (Math.PI / 2) - function;
    System.out.println("x= " + x + " y= " + result);
    System.out.println("Test " + Math.acos(Math.pow(x, 2) - 1));
}




}