Three terms of an arithmetic sequence are shown below. Which recursive formula defines the sequence?f(1) = 6, f(4) = 12, f(7) = 18

From term 1 to term 4, the value increases from 6 to 12, a total increase of 6 over 3 steps. So each step adds 6 ÷ 3 = 2. From term 4 to term 7, the same increase of 6 over 3 steps confirms the common difference is 2, so the recursive formula is f(n + 1) = f(n) + 2.

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