20+19-18+17-16+.+3-2+1
=20+(19-18)+(17-16)+...+(3-2)+1
=20+1+1+...+1+1【19到2一共是18个数,所以会产生9个1,算上最后一个+1,一共是10个1】
=20+10=30
简便计算:20+19-18+17-16+.+3-2+1
简便计算:20+19-18+17-16+.+3-2+1
数学人气:174 ℃时间:2019-12-25 10:10:19
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