Answer:
B. an = 7·13^(n-1)
Explanation:
The general form of the explicit rule for a geometric sequence is ...
an = a1·r^(n-1)
The common ratio (r) is the multiplier in the recursive rule: 13. The first term (a1) is given as 7. Filling in these values, you have ...
an = 7·13^(n-1)
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As always, you can check the answer choices to see which one satisfies the requirements. Here, you need go no further than evaluating each of the expressions for n=1.
A. a1 = 13·7² ≠ 7
B. a1 = 7·1 = 7 . . . . as required
C. a1 = 7·13² ≠ 7
D. a1 = 13·1 ≠ 7