2\1+(3\1+3\2)+(4\1+4\2+4\3)+(5\1+5\2+5\3+5\4)+.+(40\1+40\2+.
2\1+(3\1+3\2)+(4\1+4\2+4\3)+(5\1+5\2+5\3+5\4)+.+(40\1+40\2+.
1/2+1/3+2/3+1/4+2/4+3/4+1/5+2/5+3/5+4/5.+1/40+2/40+.+38/40+3
计算 1/2-(1/3+2/3)+(1/4+2/4+3/4)-(1/5+2/5+3/5+4/5)+...-(1/21+2
1/1×2+1/2×3+1/3×4+1/4×5+...+1/39×40
1/1 ,1/2 ,2/2,1/3,2/3,3/3 ,1/4,2/4,3/4,4/4 ,1/5,2/5----(找规律)
(1/2+1/3+1/4+…1/39+1/40)+(2/3+2/4+2/5+…2/39+2/40)+(3/4+3/5+3
5/9+(3/4-1/2)
判断:1/4+2/5+3/5=1/4+(2/5+3/5)对错
计算1/2+(1/3+2/3)+(1/4+2/4+3/4)+(1/5+2/5+3/5+4/5)+.+(1/50+2/50
(1/3+2/3)+(1/4+2/4+3/4)+(1/5+2/5+3/5+4/5)+.+(1/100+.99/100)=
4×(-1/2²)-3/2×(-2/5)
托式计算(有过程):1/2+(1/3+2/3)+(1/4+2/4+3/4)+(1/5+2/5+3/5+4/5)+…+(1