cos s

float cos(float x, int n)
{
int a = 8*n - 6;
int b = 4*n*n - 2*n; // 2n(2n-1)
float s = 1;

int i;

x = x*x; //x²

for(i=0;i<n;i++)
    {
    s = 1 - x*s/b;
    b -= a;
    a -= 8;
    }

return s;
}