Taylor series for cos

taylor.c

#include <stdio.h>
#include <math.h>

double my_cos(double x) {
    int n = 2;
    double result = 1;
    double x2 = x * x;
    double a = -x * x / 2;

    while (fabs(a) > 0.0001) {
        result += a;
        a = -a * x * x / (n * (n + 1));
        n += 2;
    }

    return result;
}

int main(int argc, char **argv) {
    int i;
    double x;

    printf(" x   my_cos   cos\n");
    for (i = 0; i <= 10; i++) {
        x = 0.1 * i;
        printf("%.1f %f %f\n", x, my_cos(x), cos(x));
    }

    return 0;
}