1×2×1/3+2×3×1/4+3×4×1/5+……n×(n+1)×1/(n+2)
来源:百度知道 编辑:UC知道 时间:2024/06/03 16:20:10
拜托``` 速度
什么是配凑?
什么是配凑?
令a=n×(n+1)×1/(n+2),配凑变形后得
a=n-1+2/(n+2)
n×(n+1)×1/(n+2)=[(n^2+4n+4)-(3n+6)+2]/(n+2)=(n+2)-3+2/(n+2)
再把原题中的数带入就行了
n×(n+1)×1/(n+2)=n-1+2/(n+2)
1×2×1/3+2×3×1/4+3×4×1/5+……n×(n+1)×1/(n+2)
=0+2/3+1+2/4+2+2/5+...+n-1+2/(n+2)
=(1+2+3+...+(n-1))+2(1/3+1/4+1/5+...+1/(n+2))
=n(n-1)/2+2(1/3+1/4+1/5+...+1/(n+2))
1/3+1/4+1/5+...+1/(n+2)该式无法化简了.
n年前做过
1+1/(1+2)+1/(1+2+3)+...+1/(1+2+3+...+100)
1+1/(1+2)+1/(1+2+3)+-------+1/(1+2+3+----+100)
1/1+2 + 1/1+2+3 +....+ 1/1+2+3+....+100=
1*2=1/3*1*2*3, 1*2+2*3=1/3*2*3*4
(3+1)(3^2+1)(3^4+1)...(3^2n+1)+1/2
1+1/1+2+1/1+2+3+...+1/1+2+3...+2000
1*(1/1+2)*(1/1+2+3)*~~~*(1/1+2+~~~2005)=?
3/2=2+1/1*2=1/1+1/2
(1-1/2^2)*(1-1/3^2)*(1-1/4^2).......(1-1/100^2)
1+1/2+1/3+.....+1/n