等差数列{an}a4+a6+a8+a10+a12=120.则a9-1/3a11的值为

分类: 作业答案 • 2021-11-12 22:12:05

问题描述：

答

a4+a6+a8+a10+a12=120
5a8=120
a8=24
a9-1/3*a11
=a8+d-1/3*(a8+3d)
=a8+d-1/3a8+d
=a8+1/3a8
=24+1/3*24
=24+8
=32