1-1/3-1/9-1/27-1/81-1/243-1/729=?

分类: 作业答案 • 2021-12-19 16:39:15

问题描述：

答

从第二项起等比数列，把负号提出来。公比1/3

答

1-1/3-1/9-1/27-1/81-1/243-1/729
=1-(1/3+1/9+1/27+1/81+1/243+1/729)
=1-{(1/3)*[1-(1/3)^6]/[1-(1/3)]
=1-[(728/729)/2]
=1-(364/729)
=365/729