# Math Help - Increasing sequence

1. ## Increasing sequence

Is it possible to show that the sequence defined by
$a_1 = 1, \hskip 2em a_{n+1} = 3-\frac{1}{a_n}$
is increasing without relying on mathematical induction?

2. Originally Posted by Euclid's Bridge Habitant
Is it possible to show that the sequence defined by
$a_1 = 1, \hskip 2em a_{n+1} = 3-\frac{1}{a_n}$
is increasing without relying on mathematical induction?
Almost certainly not, because the result depends on knowing that $a_1=1$. If for example $a_1=4$ then the sequence will be decreasing. In order to use information about $a_1$ to prove something about $a_{n+1}-a_n$, you need to bridge the gap between 1 and n. The only apparent way to do this is to use an inductive method.

3. Originally Posted by Opalg
Almost certainly not, because the result depends on knowing that $a_1=1$. If for example $a_1=4$ then the sequence will be decreasing. In order to use information about $a_1$ to prove something about $a_{n+1}-a_n$, you need to bridge the gap between 1 and n. The only apparent way to do this is to use an inductive method.
I might add that if you could solve the difference equation eactly, you might be able to deduce that it is increasing but this is a nonlinear difference equation and they tend to be very difficult to solve exactly.