1/(1*2*3)+1/(2*3*4)+1/(3*4*5)+.1/(26*27*28)=?

来源:学生作业帮助网 编辑:六六作业网 时间:2024/05/13 00:36:57
1/(1*2*3)+1/(2*3*4)+1/(3*4*5)+.1/(26*27*28)=?1/(1*2*3)+1/(2*3*4)+1/(3*4*5)+.1/(26*27*28)=?1/(1*2*3)+

1/(1*2*3)+1/(2*3*4)+1/(3*4*5)+.1/(26*27*28)=?
1/(1*2*3)+1/(2*3*4)+1/(3*4*5)+.1/(26*27*28)=?

1/(1*2*3)+1/(2*3*4)+1/(3*4*5)+.1/(26*27*28)=?
1/(1*2*3)=1/2*[1/1*2-1/2*3]=1/2*[(1/1-1/2)-(1/2-1/3)]=1/2*[1/1-2/2+1/3]
1/(2*3*4)=1/2*[1/2*3-1/3*4]=1/2*[(1/2-1/3)-(1/3-1/4)]=1/2*[1/2-2/3+1/4]
1/(3*4*5)=1/2*[1/3*4-1/4*5]=1/2*[(1/3-1/4)-(1/4-1/5)]=1/2*[1/3-2/4+1/5]
.
1/(26*27*28)=1/2*[1/26*27-1/27*28]=1/2*[(1/26-1/27)-(1/27-1/28)]=1/2*[1/26-2/27+1/28]
1/(1*2*3)+1/(2*3*4)+1/(3*4*5)+.+1/(26*27*28)
=1/2*{[1/1-2/2+1/3]+*[1/2-2/3+1/4]+[1/3-2/4+1/5]+...+[1/26-2/27+1/28]}
=1/2*{1-1/2-1/27+1/28}
=1/2*377/756
=377/1512