1.已知在等差数列{An}中.有A7+A9=16.A4=1.则A12的值是?

问题描述:

1.已知在等差数列{An}中.有A7+A9=16.A4=1.则A12的值是?
2.已知{An}成等差数列,求证{2An-3}也是等差数列.

1.
A12 + A4 = A7 + A9
A12 = 15
2.
设 An = a1 + (n-1)*d 是等差数列
An - An-1 = d
(2An - 3) - (2An-1 - 3) = 2d
故{2An-3}也是等差数列