4分之1乘26加0.25乘73加4分之1-搜答案-百度作业网

1/(1*2*3)+1/(2*3*4)an=1/[n(n+1)(n+2)]=[(n+2)-(n+1)]/[n(n+1)(n+2)]=1/n(n+1)-1/n(n+2)=[1/n-1/(n+1)]-(1

1乘3乘5分之4加3乘5乘7分之4+...+95乘97乘99分之4=1/(1×3)-1/(3×5)+1/(3×5)-1/(5×7)+...+1/(95×97)-1/(97×99)=1/(1×3)-1/

=[1/(1*3)-1/(3*5)]+[1/(3*5)-1/(5*7)]+.+[1/(95*97)-1/(97*99)]=1/(1*3)-[1/(3*5)-1/(3*5)]-.-[1/(95*97)-

(1*2*3+2*4*6+3*6*9+4*8*12)/(3*4*5+6*8*10+9*12*15+12*16*20)=(1*2*3)(1+8+27+64)/(3*4*5)(1+8+27+64)=(1*

3乘4乘5分之一加4乘5乘6分之1加5乘6乘7分之1加6乘7乘8分之1.98乘99乘100分之1=1/2[1/3*4-1/4*5]+1/2[1/4*5-1/5*6]+...+1/2[1/98*99-1

50/7*1/4+0.25*24/7+1/4=25/14+6/7+1/4=50/28+24/28+7/28=81/28

1乘2分之1加2乘3分之1加3乘4分之1加4乘5分之1加5乘6分之1加6乘7分之1=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7=1-1/7=6/7=7分

原式=1/2*(1/2*3-1/3*4+1/3*4-1/4*5+.+1/8*9-1/9*10)=1/2*(1/6-1/90)=1/2*(14/90)=7/90

1/(2*3)+1/(3*4)+...+1/(49*50)=1/2-1/3+1/3-1/4+...+1/49-1/50=1/2-1/50=12/25

1/2*3+1/3*4+1/4*5+……+1/49*50=(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+……+(1/49-1/50)=1/2-1/3+1/3-1/4+1/4-1/5+……

把前两项的九分之一提出来,然后再去算

答案4949/19800.n×（n+1）×（n+2）分之一=1/2｛1/n×1/（n+1）-1/（n+1）×1/（n+2）｝按上面式子每项裂开,消去之后,变成=1/2｛1/2-1/9900｝,完毕

4949/19800因为1/n(n+1)(n+2)=1/n(1/(n+1)-1/(n+2))=1/n-1/(n+1)-1/2(1/n-1(n+1))

370/4+24.5/4+5.5/4=（370+24.5+5.5）/4=100

（1×2.3×4.5+3×6.9×13.5）分之（2×4.6×9+4×9.2×18）=1×2.3×4.5×（1+3×3×3）分之【1×2.3×4.5×（2×2×2+4×4×4）】=（1+3×3×3）分

2/(1×2×3)+2/(2×3×4)+...+2/(28×29×30)=2*1/2*[1/(1×2)-1/(2×3)+1/(2×3)-1/(3×4)+...+1/(28×29)-1/(29×30)]

=1*2*3(1+2*2*2+7*7*7)/[1*3*5(1+2*2*2+7*7*7)]=1*2*3/(1*3*5)=2/5

1.26×0.25+8.74×¼=(1.26+8.74)×0.25=10×0.25=2.5