等差数列
a7,a9,等差中项 是 a8
a7 + a9 = 2a8
a4,a12,等差中项也 是 a8
a4 + a12 = 2 a8 = a7+ a9 = 16
a12 = 16 -a4 = 16 -1 = 15
已知等差数列【an]中.a7+a9=16,a4=1.则an12等于
已知等差数列【an]中.a7+a9=16,a4=1.则an12等于
是a12等于多少
是a12等于多少
数学人气：774 ℃时间：2020-05-05 22:12:10
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