Question

高二等差数列题！！！！！！！！！！！！急！！！！！！！！！！

在等差数列{AN}中

已知A6=10 S5=5 求A8和S8

Answer 1

S5 = 5*A3 = 5
所以A3 = 5/5 = 1

因为A6 = 10，所以公差d = (A6 - A3)/3 = (10 - 1)/3 = 3
所以
A8 = A3 + 5d = 1 + 5*3 = 16
S8 = 4*(A4 + A5) = 4*(1+3+1+3+3) = 44