1+2···+99
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1+2···+991+2···+991+2···+99首项加末项=100,一共有49对,外加剩余的50,所以1+2···+99=100*49+50=49504950100x(99/2)5000这个要用
1+2···+99
1+2···+99
1+2···+99
首项加末项=100,一共有49对,外加剩余的50,所以1+2···+99=100*49+50=4950
4950
100x(99/2)
5000
这个要用等差数列求和公式：首项加末项的和乘公差除以二
100*49+50
1+99=100
2+98=100
3+97=100
........................
.......................
99+1=100
将这99个式子相加得：
2(1+2+3+...+99)=100*99
(1+2+3+...+99)=100*99/2=4950
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···+99
1+2+3+4·······+98+99等于多少
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··························
计算1-2+3-4+5-6+······+99-100=
计算：(2+4+6+8+···+100)-(1+3+5+···+99)
1+2+3+······+98+99+100=?
计算1-2+3-4+5-6+······-98+99=
1+2+3+······+95+96+97+98+99=?
(2+4+6+8+······+100)—(1+3+5+7+······+99)等于几
1+（-2）+3+（-4）···········+99-100等于多少
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,
巧算：100+99-98-97+96+95-·····+4+3-2-1
100+99-98-97+96+95+·······+4+3-2-1怎么做?
1/100+2/100+3/100·······98/100+99/100怎样算?
计算：（-1）+(+2)+(-3)+(-4)+.+(-99)+(+100)+.+(-2009)+(+2010)快点··········很急