分母裂项拆分万能公式:
1.1/[n(n+1)]=(1/n)- [1/(n+1)]
2.1/[(2n-1)(2n+1)]=1/2[1/(2n-1)-1/(2n+1)]
3.1/[n(n+1)(n+2)]=1/2{1/[n(n+1)]-1/[(n+1)(n+2)]}
裂项法求和公式:
1. 1/[n(n+1)]=(1/n)- [1/(n+1)
2.1/[(2n-1)(2n+1)]=1/2[1/(2n-1)-1/(2n+1)]
3.1/[n(n+1)(n+2)]=1/2{1/[n(n+1)]-1/[(n+1)(n+2)]}