Question

等差数列的前n项的和为sn,若S(2m-1)/(2m-1）=10,则am

Answer 1

S(2m-1)/(2m-1）=10

即 a1*（2m-1）+ [（2m-1）*（2m-1-1）/2]*d

-------------------------------------------------------- = 10

2m-1

解得 a1 +（m-1）d=10

am=a1+(m-1)d=10