Bens4vcobra wrote:In the infinite sequence a1, a2, a3....aN.... each term after the first is equal to twice the previous term. If a5 - a2 = 12 what is a1?
A) 4
B) 24/7
C) 2
D) 12/7
E) 6/7
We can plug in the answers, which represent the value of a1.
Answer choice C: a1 = 2.
Since each term is equal to twice the previous term:
a2 = 4, a3 = 8, a4 = 16, and a5 = 32.
a5-a2 = 32-4 = 28.
Too big: the difference is supposed to be 12, which is less than 1/2 of 28.
Thus, the correct answer must be less than 1/2 the value of answer choice C.
Thus, the correct answer must be less than 1.
The correct answer is
E.
Answer choice E: a1 = 6/7.
a2 = 12/7, a3 = 24/7, a4 = 48/7, and a5 = 96/7.
a5-a2 = 96/7 - 12/7 = 84/7 = 12.
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