等差数列{An}中,若A1004+A1005+A1006+A1007+A1008=10,则S2011=?
问题描述:
等差数列{An}中,若A1004+A1005+A1006+A1007+A1008=10,则S2011=?
答
A1004+A1005+A1006+A1007+A1008=10
数列An为等差数列,则:
A1004+A1008=A1005+A1007=2A1006
即5A1006=10
A1006=2
而A1+A2011=2A1006=4
S2011=2011(A1+A2011)/2=4022