脑算实例连载29

脑算实例连载29

廿、两位数的平方差：大数加小数，乘大数减小数。

     76²-24²＝（76+24）×（76-24）                49²-36²＝85×13

            ＝5200                                       ＝1105

     62²-52²＝（62+52）×（62-52）                82²-43²＝125×39

            ＝1140                                       ＝4875

     65²-42²＝107×13                             98²-86²＝184×12

            ＝1391                                       ＝2208