500-1-2-3-········-76-77-78.怎么算?要巧算.

来源:学生作业帮助网 编辑:作业帮 时间:2024/05/02 14:09:35
500-1-2-3-········-76-77-78.怎么算?要巧算.

500-1-2-3-········-76-77-78.怎么算?要巧算.
500-1-2-3-········-76-77-78.怎么算?要巧算.

500-1-2-3-········-76-77-78.怎么算?要巧算.
因为1 + 2 + 3 +---- +76+77+78
和78+77+76+-----+3 + 2 + 1 两式的和相等,并且以上两式对应上下相加1+78=79,有78个79.所以一个式子的和为(1+78)×78÷2.故
500-1-2-3-········-76-77-78
=500-(1+2+3+----+76+77+78)
=500-(1+78)×78÷2
=500-79×39
=500-3081
=-2581

500-(1+78)*78/2=-3144

1 2 3 4 ·····7 ·······10 ········?1 3 5 7 ·····?······?··········290 1 4 9 ·····?······?··········? 急·····················1+2+3+...+999=? 计算1/(1*4)+1/(4*7)+1/(7*10)+------+1/(97*100)································································································ 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,······.5非学无以广才,······.6······,福兮祸之所伏.7项庄舞剑,······.8······,人以群 8+11+14+17+20+·······+305 数学计算题.呜呜呜1+2+3+4+···················+98+99+100+99+98+···············+3+2+1 1+2++3+··········+10000= 将下列每个3*3正方形内的九格以及横竖九格均填入一至九的数字,且不重复.· 8 9 · 2 ··1··· 1 ··· 3······· 6 7········· 8 2·········5 ···· 7 ··············· 9 8 ····7 · 观察下列三角形数表其中从第二行起每行的每一个数为其肩膀上两树之和则该表的最后一个数是?1 2 3 4 5 6 7 8················ 97 98 99 100 3 5 7·························· 全部属于裸子植物的是 1卷柏 2侧柏 3银杏 4刺槐 5苏铁 6梧桐 7云杉 8贯从 9珙桐 A1237 B2357 C2379 D1358贯从是贯众······························· 纸鹤数量的意义比如说 1只纸鹤,代表······· 2只纸鹤,代表······· ······················· ···························· ·················· 越多越好, 秦始皇和汉武帝各自的功劳是?(用1·······2·······3··········来说) 2011红领巾快乐数独答案一2·····4·9·631·4·8·8··97··3··3··2·95···95·86···15·3··7··9··47··5·7·3·182·3·4·····7二7·1·8·3·····413·6·2·6···4·8·8·5·1·2·61·····94·2·9·4·7·8· 变态数学题·······方程一道············x+2y+3z=1x=y+12x+3y+5z=2方程组············要过程············我解了之后总觉得无解····· 带有数字的四字词语按顺序1···2···3···4···5···6···7···8···9···10···祝福语 在等腰三角形ABC中,AB=AC.求证1、∠BAD=∠CAE 2、如果AD=AE,那么BD=CE吗?急啊························································· 把1 9填入81格方框,不能重复· · 4 · · 5 · 6 ·9 · · 3 · · · 5 17 · · 6 · · · · 3· · 9 · 1 6 · 4 ·· 2 · 4 · · · 8 ·· 4 · 7 · · 5 · ·5 · · · · 7 · · 84 1 · · · 8 · · 5· 8 · 9 · · 6 · 4 (2+4+6+8+······+100)—(1+3+5+7+······+99)等于几 (1+3+5++7+9······+2011)-(2+4+6+8······+2012)=