Suppose we have an infinite sequence
and that for all we have
(1) |
where is a positive integer.
In the main article we claimed that in this case the ratio of successive terms of the sequence converges to the metallic mean . We’ll now give you a justification of this claim. Recall that
(2) |
Substituting the expression given by this equation for the in the denominator on the right hand side of the same expression gives
Another substitution gives
Continuing on in this vein, it is not too hard to prove that is equal to the infinite continued fraction
(You can find out more about continued fractions here.)
Now back to our sequence. The ratio of successive terms is
By equation (1) this is equal to
Now
Applying equation (1) to the term we get
You can see the picture: continuing to make substitutions according to equation (1), we end up with a finite continued fraction expression for of the form
Letting tend to infinity we can then prove that the ratio of successive terms in the sequence converges to infinite continued fraction
Which, as we have sketch-proved above, is equal to