青海健翔集团南雪迅:脑算实例连载29

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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