SOLUTION: Find an explicit rule for the nth term of a geometric sequence where the second and fifth terms are -36 and 2304, respectively. (2 points)
an = 9 • 4n
an = 9 • (-4)n +
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Question 1134911: Find an explicit rule for the nth term of a geometric sequence where the second and fifth terms are -36 and 2304, respectively. (2 points)
an = 9 • 4n
an = 9 • (-4)n + 1
an = 9 • 4n - 1
an = 9 • (-4)n - 1
5
Answer by greenestamps(13200) (Show Source): You can put this solution on YOUR website!
Use "^" to denote exponentiation; and use parentheses where required. The four answer choices should be
a(n) = 9*4^n
a(n) = 9*(-4)^(n+1)
a(n) = 9*4^(n-1)
a(n) = 9*(-4)^(n-1)
The 2nd and 5th terms are opposite signs, so the common ratio has to be negative; so the first and third answer choices can't be right.
The first term is -36.
The second answer choice gives a(2) = 9*(-4)^3 = 9*-64 = -576. not right.
The fourth answer choice gives a(2) = 9*(-4)^1 = 9*(-4) = -36. right.
The problem is more educational if you aren't given answer choices....
The 5th term 2304 is the 2nd term -36, multiplied by the common ratio 3 times:
--> the common ratio is -4
The 2nd term, -36, is the first term, multiplied by the common ratio once:
--> the first term is 9
The n-th term is the first term, multiplied by the common ration (n-1) times:
... which is the 4th answer choice
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