1\(2\3)\(3\4)······\(18\19)\(19\20)=
1\(2\3)\(3\4)······\(18\19)\(19\20)=
(1-2)×(2-3)×(3-4)×······×(19-20)=
1×2×3+2×3×4+3×4×5+·······+18×19×20=35910
用简便方法计算 20-19+18-17+··· ···+4-3+2-1
(20平方+18平方+16平方+······+2平方)—(1平方+3平方+5平方+······19平方)
1+2++3+··········+10000=
计算:(1-1/21)×(1-1/20)×(1-1/19)×(1-1/18)×······(1-1/3)×(1-1/2)
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,······.
计算1×2²+2×3²+3×4²+4×5²+······+18×19²
1·2·3·4+1=5²; 2·3·4·5+1=11²; 3·4·5·6+1=19²;
1+2+3+4+5+6······38+39=?
1+2+3+4··· ···+78+79=?