In the arithmetic sequence an, the tolerance d = 1 / 2, A4 + A17 = 8, then A2 + A4 + A6 + +a20=?s20=?

In the arithmetic sequence an, the tolerance d = 1 / 2, A4 + A17 = 8, then A2 + A4 + A6 + +a20=?s20=?

∵ arithmetic sequence and A4 + A17 = 8 ∵ a1 + 3D + A1 + 16d = 8 ∵ A1 = - 3 / 4A20 = a1 + (20-1) × d = 35 / 4S even = A2 + A4 + A6 + +A20s odd = a1 + a3 + A5 + +A19 = s-even-10d = s-even-5 ℅ S20 = 20 × (- 3 / 4 + 35 / 4) / 2 = 80 ∵ S20 = s-even + s odd = 80 ∵ s-even + s-even-5 = 80 ∵ s-even = 85 / 2, i.e. A2 + A4 +

If the tolerance of the arithmetic sequence {an} is 2 and the sum of the first 20 items is 150, then A2 + A4 + A6 + +a20=______ ．

∵ the tolerance of arithmetic sequence {an} is 2, the sum of the first 20 terms is 150, ∵ s odd + (s odd + 10 × 2) = 150, s odd = 65, ∵ A2 + A4 + A6 + +A20 = 150-65 = 85

Let (an) be an arithmetic sequence with positive tolerance, if a1 + A2 + a3 = 15, A1 * A2 * A3 = 80. Find S33

Set tolerance = M
A1=A2-m
A3=A2+m
So 3 * A2 = 15
A2=5
So (5-m) * 5 * (5 + m) = 80
M = + 3 (- 3 rounding off)
So A1 = 2, A2 = 5, A3 = 8