Proving a monotonic sequence is unbounded

  • Thread starter Thread starter alligatorman
  • Start date Start date
  • Tags Tags
    Sequence
alligatorman
Messages
113
Reaction score
0
I'm trying to prove that the sequence
x_1,x_2,_\cdots
of real numbers, where
x_1=1 and x_{n+1}=x_n+\frac{1}{x_n^2} for each n=1,2, \cdots

is unbounded.

(sorry for the ugly latex! i don't know if there's a way to format that better)

I'm thinking of proving by contradiction, assuming it is bounded and then somehow getting it to imply that the sequence is not increasing, but I'm not sure how to go about it.

Any hints?
 
Physics news on Phys.org
If it were bounded, it would converge.
 
And if it were to converge to, say, x, that limit would satisfy
x= x+ \frac{1}{x}
What values of x satisfy that?
 
HallsofIvy said:
And if it were to converge to, say, x, that limit would satisfy
x= x+ \frac{1}{x}
What values of x satisfy that?

:confused: I don't understand why this is true.
 
Start with x_{n+1}= x_n+ 1/x_n and take the limit, as n goes to infinity ,of both sides. If the sequence {x_n} converges to some number, x, then each "x_n" or "x{n+1}" term will go to x.
 
Back
Top