1*2/1 + 2*3/1 + 3*4/1 +.+29*30/1 /是分号,*乘号,1 1 1 1 --- + --- + --- + .+----- = 1*2 2*3 3*4 29*30
问题描述:
1*2/1 + 2*3/1 + 3*4/1 +.+29*30/1
/是分号,*乘号,1 1 1 1 --- + --- + --- + .+----- = 1*2 2*3 3*4 29*30
答
注意到:1/1*2=1-1/2 1/2*3=1/2-1/3 1/3*4=1/3-1/4 ...原式=1-1/2+1/2-1/3+1/3-1/4+...+1/29-1/30 =1-1/30=29/30