初一的数学题，用简便方法计算的题目

1．－2.7x56＋7.9x（－56）＋6x5.6

－（1／90）．呢那么;nx（n＋1）呢？
（－1／2）－（1／6）－（1／12）－⋯？告诉我过程，为什么这么做？

1x2＋2x3＋3x4＋⋯，请问1x2＋2x3＋3x4＋⋯＋100x101等于多少

－2.7x56＋7.9x（－56）＋6x5.6
=－2.7x56-7.9x56＋(6÷10)x(10x5.6)
=－2.7x56-7.9x56＋0.6x56
=56x(-2.7-7.9+0.6)
=56x(-10)
=-560

－2.7x56＋7.9x（－56）＋6x5.6 =0.6x56－2.7x56-7.9x56 =56x(0.6-2.7-7.9) =56x(-10) =-560

原式=-56*(2.7+7.9-0.6)=-56*10=-560 1x2＋2x3＋3x4＋⋯＋100x101 可以看出每2项合并后的规律，原式=2（2×2+4×4+6×6+。。。。+100×100） =2（2^2+4^2+6^2+.....+100^2) =2*(100*51*101)/3=343400

（3/5-1/2-7/12)乘（60*3/7-60*1/7+60*5/7)

=（3/5-1/2-7/12)乘（3/7-1/7+5/7)×60

=（3/5-1/2-7/12)×1×60

=3/5×60-1/2×60-7/12×60

=36-30-35

= -29

13除1.5-0.34除3又1/3+1/3除1/13-0.34除1又2/5

=13除3/2-0.34除10/3+1/3除1/13-0.34除7/5

=13×2/3-0.34×3/10+1/3×13-0.34×5/7

=13×2/3+1/3×13-0.34×3/10-0.34×5/7

=13×(2/3+1/3)-0.34×(3/10+5/7)

=13-0.34×71/70

-149又3/40乘20

=(-149-3/40)乘20

= -298-3/2

= -299-1/2

=-299又1/2

99又24/25乘（-5）

=99×（-5）+24/25×（-5）

= -495-24/5

= -499-4/5

= -499又4/5

-2.7x56＋7.9x（－56）＋6x5.6 =-2.7×5.6×10+7.9×（-5.6）×10+6×5.6 =-27*5.6-79×5.6+6×5.6 =5.6×（-27-79+6） =5.6×（-100） = - 560

2)-(1/3 当n=100时，就有;(2×3)+1/+n) =(1²9-1/.7+7;3+1/10] =-(1-1/.9-0;(1×2)+1/3=343400 (-1/+…+n².6 =-(2.7×56+7.9×(-56)+6×5.6 =-2;4+…+1/(3×4)+…+1/+1)+(2²+3)+…+(n²-2;+2)+(3².6)×56 =-10×56 =-560 1×2+2×3+3×4+…+n(n+1) =(1²3-1/.7×56-7.9×56+0：1×2+2×3+3×4+…+100×101=100×101×102/.6×5;2+1/12)-…-(1/90) =-(1/2+1/6+1/12+…+1/)+(1+2+3+…+n) =n(n+1)(2n+1)/6+n(n+1)/2-1/2 =n(n+1)/6×(2n+1+3) =n(n+1)(n+2)/90) =-[1/6)-(1/(9×10)] =-[1-1/+2²+3²