C++関数テイラー式でsinxのcosx値を求める

#include"iostream"
#include "Cmath"//     ，     ；
using namespace std;
double mysin(double);//   
double mycos(double);
double myabs(double);     //        ；


const int pi = 3.1415926;


int main()

{
	cout << "        sin(3.14/2)   ：" << sin(pi / 2) << endl;
	cout << "      sin(3.14/2)   ：" << mysin(pi / 2);

	cout << "    sin(56')   " << mysin((56.0/180)*pi)<< endl;
	cout << "     sin(56')   " << sin((56.0 / 180)*pi) << endl;


	cout << "        cos(87)" < 1e-5);
	return sum;


}
double mycos(double x)
{
	double sum = 1,x_pow = 1, item;
	int n = 0, fact = 1, sign = -1;


	fact = fact*(n + 1)*(n + 2);
	item = x_pow / fact*sign;
	x_pow *= x*x; fact;
	sum += item;
	sign = -sign; //               ；
	
	n += 2;

	return sum;
}
double myabs(double x)
{
	return ((x >= 0 ? x : -x));
}