It's not good to be beaten by others if it's late.
1.a3+a7-a 10=8，a 1 1-a4=4
a3=a 1+2d a7=a 1+6d ……
a 1-d=8 7d=4 a 1=60/7
s 13 = 13a 1+ 13 * 12 * d/2 = 156
2 . a4a 6+2a5a 7+a6a 8 = 36 = a5^2+2a5a7+a7^2=36
(a5+a7)^2 =36
a5+a7=6
3. When n = 12345, |an|=an n= 6 7 8 9 10 |an|=-an.
a 1-a6 =-5d = a2-a7 =……= a5-a 10
S 10= -25d =50
4. The process of nkai11power-1 is a1(1+q)1= a12a/kloc-0.
5. because of d
When Sn takes the maximum value, n=5 or 6.