static internal double GetCos(this Point oldpoint, Point newpoint)
{
double pc = oldpoint.ProduitCartesien(newpoint);
return pc / (oldpoint.Longueur() * newpoint.Longueur());
}
static internal double GetSin(this Point oldpoint, Point newpoint)
{
double Det = oldpoint.Determinant(newpoint);
return Det / (oldpoint.Longueur() * newpoint.Longueur());
}