1/1*2 1/2*3 1/3*4 ....... 1/20
|1/2-1|+|1/3-1/2|+|1/4-1/3|+...+|1/2012-1/2011|+|1/2013-1/20
1/2*1/3+1/3*1/4+1/4*1/5.+1/18*1/19+1/19*1/20
1/1*2*3+1/2*3*4+1/3*4*5+.+1/18*19*20
1/1*2*3 + 1/2*3*4 + 1/3*4*5 +.+1/20*21*22
1 1/2+2 1/6+3 1/12+4 1/20+.20 3Q
1/1*3+1/2*4+1/3*5+1/4*6+.+1/18*20
1-2/1*(1+2)-3/(1+2)*(1+2+3)-4/(1+2+3)*(1+2+3+4)-……-20/(1+2+3
1*1/2+1/2*1/3+1/3*1/4……1/19*1/20
1/1×2+1/2×3+1/3×4+...+1/19×20等于多少
2/1 3/1 4/1 5/1 6/1 8/1 10/1 12/1 15/1 20/1
1 1 1 1 2 1 1 3 3 1 1 4 6 4 1 1 5 10 10 5 1 1 6 15 20 15 6 1
1/2*3+1/3*4+1/4*5+1/5*6.+1/19*20