如题所述
第1个回答 2020-04-17
合并同类项,加号左右两边都有39
(38+1)×39
=39×39
=(40-1)×39
=40×39-39
=1560-39
=1521
(38+1)×39
=39×39
=(40-1)×39
=40×39-39
=1560-39
=1521
第2个回答 2020-04-17
简便计算
38×39+39
=39×(38+1)
=39×39
=39×(40-1)
=39×40-39
=1560-39
=1521本回答被网友采纳
38×39+39
=39×(38+1)
=39×39
=39×(40-1)
=39×40-39
=1560-39
=1521本回答被网友采纳
第3个回答 2020-04-17
此类型的题意在考查提取公因数,所以可变为39×(38+1)=39×39=39×40-39=1521
第4个回答 2020-04-17
解,原式=(38+2)×39-39
=40×39-39
=1560-39
=1521
=40×39-39
=1560-39
=1521
第5个回答 2020-04-17
38×39+39
=39×(38+1)
=(40-1)×(40-1)
=40×40-40×1-1×40+1×1
=1600-40-40+1
=1521
=39×(38+1)
=(40-1)×(40-1)
=40×40-40×1-1×40+1×1
=1600-40-40+1
=1521