已知数列{an}是等差数列,其前n项和为Sn,若a6=2,S5=30,求s8

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已知数列{an}是等差数列,其前n项和为Sn,若a6=2,S5=30,求s8
已知数列{an}是等差数列,其前n项和为Sn,若a6=2,S5=30,求s8

已知数列{an}是等差数列,其前n项和为Sn,若a6=2,S5=30,求s8
a[n]等差数列所以：S[5] = 5 * a[3] = 30,a[3] = 6 a[6] - a[3] = 3d,2 - 6 = 3d,d = -4/3 a[4] = 6 - 4/3 = 14/3 a[5] = 6 - 2 * 4/3 = 10/3 所以S[8] = 4 * (a[4] + a[5]) = 4 * 8 = 32

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