3乘5除以1加5乘7除以1加到1998乘1999除以1

1/2X3X4X5+1/3X4X5X6+1/4X5X6X7.1/97X98X99X100=?=1/3[1/2*3*4-1/3*4*5]+1/3[1/3*4*5-1/4*5*6]+1/3[1/4*5*6

45乘3除以5加7减10(8乘9)=45×3÷5+7-10×(8×9)=27+7-720=34-720=-686

裂两项相消法：完全是凑出简单的几项和差的形式进行化简：步骤一：待定系数法-----设An=1/[n(n-1)(n-2)];(n>=3,n∈N*)；令An=A/(n-2)+B/(n-1)+C/n;通分后

1/14÷3/5-1/3×5/14+3/7=1/14×5/3-1/3×5/14+3/7=5/14×1/3-1/3×5/14+3/7=3/7

原式=(1/2)×(1-1/3)+(1/2)×(1/3-1/5)+(1/2)×(1/5-1/7)+……+(1/2)×(1/2005-1/2007)=(1/2)×(1-1/3+1/3-1/5+1/5-1

原式=X/(1*2)+X/(2*3)+X/(3*4)+……+X/(2008*2009)(提取公因式X)=X(1/(1*2)+1/(2*3)+1/(3*4)……+1/(2008*2009)(裂项相消)=

0.325乘0.8加0.55除以5/4减3/5除以8/7=0.325×0.8+0.55×4/5-3/5×7/8=（0.325+0.55）×0.8-3/5×7/8=7/8×0.8-3/5×7/8=7/8

原式通项可以写成1/(n*(n+1)*(n+2))n=1,2,...,2000原式n从1到2000上述各项的和.而1/(n*(n+1)*(n+2))=(1/n)+(1/(n+1))-(2/(n+2))

原式=1x2x3+2x3x4+3x4x5+...++7x8x9=6+24+60+120+210+336+504=1260

4又5分之1乘25加32又7分之4除以4加0.25乘125=（4+1/5）×25+(32+4/7)÷4+0.25×125=100+5+8+1/7+125/4=113+1/7+31+1/4=144+4/

4.5625

5/13x1/7+6÷13x1/7+2/13÷7=5/13x1/7+6/13x1/7+2/13x1/7=1/7x（5/13+6/13+2/13）=1/7x1=1/7（7分之1）亲,请【采纳答案】,您的

5*(3/5+2/7)*7=5*7*(21/35+10/35)=35*31/35=314/9*13+7/9/(1/13)-13=4/9*13+7/9*13-13=11/9*13-13=2/9*13=2

1/4*5+1/5*6+1/6*7+1/7*8=5/4+6/5+7/6+8/7=1+1/4+1+1/5+1+1/6+1+1/7=4+319/420=1999/420再问：要简单的算式过程。得数好像不是

1的平方加2的平方加3的平.加n的平方等于n（n+1）（2n+1）/6

1/[n*(n+1)*(n+2)]=[1/n-1/(n+1)]/(n+2)=[1/n-1/(n+2)]/2-[1/(n+1)-1/(n+2)]=[1/n-2/(n+1)+1/(n+2)]/21/(1*

答案是9再问：过程再答：1×3×24+2×6×48+3×9×72=9×(1×2×4+2×4×8+3×6×12)再答：约分即可再答：分子每一个都是分母相应项的9倍再问：.....再问：要过程。再答：1×

6.4乘125%加1又5分之3除以(1减5分之1)加2乘1.25=6.4乘125%加1又5分之3×1.25加2乘1.25=（6.4+1.6+2）×1.25=10×1.25=12.5

7.2×[（7.8+1/5）÷0.4]=7.2×[（7.8+0.2）÷0.4]=7.2×（8÷0.4）=7.2×20=144（6.9-3.14）÷0.3×0.8=3.76÷0.3×0.8=(188/1

1×2+3-4+5÷6÷7=1?