1995+1996+1997+···+2004+2005-2000速算与巧算.

2000-1999+1998-1997+1996-1995+1994-1993+······+4-3+2-1咋做?第等式回答,急. 1+2-3-4+5+6-7-8+9+10-11-12+13+······+1994-1995-1996+1997快 1995+1996+1997+···+2004+2005-2000速算与巧算. 2-1三分之一+4-3三分之一+6-5三分之一+···+1996-1995三分之一+1998-1997三分之一说明每步的理由 1.（1998+1996+1994+······+4+2）-（1+3+5+······+1995+1997）=（ ）2.1+2+3+4+5+······+〇=〇43.共有四人进行跳远、百米、铅球、跳高四项比赛,规定每个单项第一名记5分,单项第二名记3分,单项第 1998+1997减1996减1995+1994+1993减1992减1991+·····+198+197减196减195麻烦说明过程,为什么要这样做, 有2个数学题用简便做大哥大姐帮帮忙!⑴1/（1*）+1/（5*7）+······+1/（1995*1997）+1/(1997*1999)⑵1/（2*7）+1/(7*12）+1/（12*17）·····+1/（92*97）+1/（97+102） 1）、40+42+44+46+······+178+180=?（2）、9999*1111*3333*6667=?（3）、1995*19961996-1996*19951995=? (1+3+5·····+1995)-2乘(2+4+6+·····+1994)= 1、在1,2,3···1996,1997 这1997个自然数中,含有数字1的自然数共有多少个?2、111···1}100个1与999···9}100个9相乘,积中有几个数字是奇数?3、1×2×3···×49×50的积,末尾有几个0?感谢zhangweizmy的回答. 1997×1997+1996×1996-1997×1996-1996×1995 简便运算 急·····················1+2+3+...+999=? 1 2 3 4 ·····7 ·······10 ········?1 3 5 7 ·····?······?··········290 1 4 9 ·····?······?··········? 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, 1.（2+5+8+11+····+1997）-（1+4+7+····+1996）=?2.有一架天平,只有5克和30克砝码,要把盐分成3等份,最少称几次?3.18分之13的分母减去12,分子应减去（ ）才能使分数值不变.3.一个底面是正方体的长 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························································· 有理数a、b在数轴上位置如图所示,试化简 |a-b|-|a+b|+2|b-2a|··········································b 0 a 3.5--6x=2x--8.7的x的值作业急啊·······················································