如题所述
第1个回答 2017-03-26
298x21=,39X49=
第2个回答 2017-03-26
=(1000-1)X21
=1000X21-1X21
=21000-21
=20979本回答被网友采纳
=1000X21-1X21
=21000-21
=20979本回答被网友采纳
第3个回答 2017-03-26
=(1000-1)×21
=1000×21-1×21
=21000-21
=20979
=1000×21-1×21
=21000-21
=20979