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Recurrence Relation 
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#1
Sep2710, 04:28 AM

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P: 1,951

1. The problem statement, all variables and given/known data
Let's say I had this recurrence relation: [tex]log\left(f\left(x+2\right)\right) = log\left(f\left(x+1\right)\right) + log\left(f\left(x\right)\right)[/tex] How do I prove, then, that... [tex]f\left(x\right) = e^{c_1 L_x + c_2 F_x}[/tex] ? 2. Relevant equations There probably are some, but I don't know any. 3. The attempt at a solution I've gotten the equation to remove the logs, but I just get... [tex]f\left(x+2\right) = f\left(x+1\right)f\left(x\right)[/tex] I don't know where to go from there. 


#2
Sep2710, 06:54 AM

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Thanks
PF Gold
P: 39,568

First, use the properties of the logarithm to get rid of the logarithm:
[tex]log(f(x+ 2))= log(f(x+1))+ log(f(x))= log(f(x+1)f(x))[/tex] and, since log is onetoone, f(x+2)= f(x+1)f(x). It's certainly true that the formula you gives satisfies that. Can you prove the solution is unique? 


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