Matt HW Method

double arctan(double x){
    double result;
    double prev;
    n = 0;

    while(abs(result - prev) > 0.000000000000001){
        prev = result;
        result = ( ((-1)^2) / (2*n+1) ) * (x^(2*n+1));
        n++;
    }

    return result;
}