(1-2)×(2-3)×(3-4)×······×(19-20)=
1\(2\3)\(3\4)······\(18\19)\(19\20)=
(1-2)×(2-3)×(3-4)×······×(19-20)=
1+2++3+··········+10000=
1×2×3+2×3×4+3×4×5+·······+18×19×20=35910
俗语和名句的填空1······,自知之明.2······,行必果.3工欲善其事,······.4临渊羡鱼,······.
用简便方法计算 20-19+18-17+··· ···+4-3+2-1
1+2+3+4+5+6······38+39=?
1+2+3+4··· ···+78+79=?
计算1-2+3-4+5-6+······-98+99=
1+2+3+4+5······+100+101=几
1/3+2/3=1,但0.333···+0.666···=0.999···,为神马?额······谁能解释一下·····
数列 1/2,3/2,1/3 ,4/3,·········1/n+1,n+2/n+1,·········是否有极限?