设等差数列{an}中,若a6=2,且S5=30,则S8=
人气：227 ℃ 时间：2020-05-15 12:36:26
解答
S5=a1+a2+a3+a4+a5=5a3=30
a3=6=a1+2d
a6=2=a1+5d
d=-4/3
a1=26/3
S8=a1+a2+a3+a4+a5a+a6+a7+a8=S5+3a7=30+3a1+18d=30+26-24=32
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