Bunuel wrote:
If \(a_n=f(n)\) for all integers n>0, is \(a_4>a_8\)?
(1) \(a_5=13\)
(2) f(x)=9−f(x−1) for all integers x
Kudos for a correct solution.
1) not sufficient.
2) a(5) = f(5) = 9-f(4) --> not sufficient.
1+2) Since f(x) = 9 - f(x-1) ---> f(x)+f(x-1) = 9. Substituting and working with the equations we get that f(4)=f(8) --> a(4)=a(8)
Answer B.
**edited after spotting a procedural error
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