If the first four terms of a sequence are (2,7,12,17), what can be a simple rule for (a_n)?

Correct answer: \(a_n=5n-3\)

The differences between consecutive terms are \(7-2=5\), \(12-7=5\), and \(17-12=5\), so this is an arithmetic sequence with common difference \(d=5\). Since \(a_1=2\), \(a_n=a_1+(n-1)d=2+5(n-1)=5n-3\). In option B, putting \(n=1\) gives 7, so it is incorrect. Exam tip: check the common difference first, then verify a rule by substituting \(n=1\).