999×99×9
=(1000-1)×99×9
=1000×99×9-99×9
=1000×(100-1)×9-(100-1)×9
=1000×100×9-1000×9-100×9+9
=900000-9000-900+9
=890109
999×99×9用简便方法详细方法
999×99×9
=(1000-1)×99×9
=1000×99×9-99×9
=1000×(100-1)×9-(100-1)×9
=1000×100×9-1000×9-100×9+9
=900000-9000-900+9
=890109