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Sequence problem, a1, a2,..an....

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by stormier » Mon Feb 07, 2011 7:49 pm
neilcao wrote:The sequence a1, a2,....an,.../ is such that an=4an-1 - 3,for all integers n>1. If ac=x, then a1=?

A. 4x-3
B. 16x-15
C. X+3/4
D. X+3/16
E. X+15/16


Is there any quick way to solve this problem?

Thanks
ac in the question stem is supposed to mean a3.

a3 = 4a2 -3 = 4(4a1-3)-3 = 16a1-15 = x

=> a1 = (x+15)/16
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