public void Rotate(double alpha)
{
P1.Rotate(alpha, Center);
P2.Rotate(alpha, Center);
P3.Rotate(alpha, Center);
P4.Rotate(alpha, Center);
}
/// <summary>
/// Returns a new <see cref="Quadrangle"/> rotated by <paramref name="rotation"/> around the origin.
/// </summary>
/// <param name="rotation">The angle to rotate by in degrees.</param>
/// <returns>The rotated <see cref="Quadrangle"/>.</returns>
public Quadrangle Rotate(float rotation)
{
return(new Quadrangle(
P1.Rotate(rotation), P2.Rotate(rotation),
P3.Rotate(rotation), P4.Rotate(rotation)));
}