Wednesday

May 25, 2016
Posted by **Terfa sakaa** on Sunday, October 14, 2012 at 4:28am.

- Math -
**drwls**, Sunday, October 14, 2012 at 6:13amI assume that "a,p" stands for arithmetic progression. Let the nth term be an.

Since a4 + a6 = 2 a5, a5 = 21.

Since a3 + a9 = 2 a6, a6 = 26

The common difference is

a(n+1) - an = a6 - a5 = 5.

The first term is 1, and the progression is

a1 = 1, a2 = 6, a3 = 11, a4 = 16,

a5 = 21, a6 = 26, a7 = 31, a8 = 36,

a9 = 41, a10 = 46...

The sum of the first 10 terms is

7 + 27 + 47 + 67 + 87 = 235