If the first n terms of the equal ratio sequence {an} and Sn = 3N + R, then r = () A. 0B. -1C. 1D. 3

∵ Sn = 3N + R, sn-1 = 3n-1 + R, (n ≥ 2, n ∈ n +), ∵ an = sn-sn-1 = 2 · 3n-1, and A1 = S1 = 3 + R. from the general term, A2 = 6, common ratio is 3, ∵ A1 = 2, ∵ r = - 1

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