A question in prooving function convergence

In summary, the conversation focused on proving that the sequence an = (an+1)/(an+2) is decreasing and finding its limit. The initial solution showed that the sequence is bounded below and has a limit. Then, the conversation delved into finding the limit by recognizing that (x+1)/(x+2)= 1- 1/(x+2). The conversation also discussed solving t= (t+1)/(t+2) and getting two solutions, but only one of them was the limit of the sequence. The expert was unable to provide a solution to the problem, as it required further understanding and steps.
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  • #2
a0= 1, an+1= (an+ 1)/(an+ 2)

I take it you want to prove that it is decreasing. It's clearly bounded below (by 0), so it has a limit. And then find the limit. a1= (1+ 1)/(1+ 2)= 2/3< 1. That you have.

Now, suppose, for some k, ak> ak+1. Then ak+1+1= (ak+1+1)/ak+1+ 2). Again you have that but, as you say, since both numerator and denominator are larger than in ak+1, that doesn't tell you anything. Perhaps it would help to recognise that (x+ 1)/(x+ 2)= 1- 1/(x+ 2). If uk+1< uk then uk+1+ 2< uk+ 2 so 1/(uk+1+ 2)> 1/uk and then -1/(uk+1)< -1/uk.

You then solve t= (t+1)/(t+2) and get two solutions. Of course, only one of those is the limit of the sequence. The fact that only one of them is positive should make it clear which!
 
  • #3
i tried to use what you told me
i have written your explanation several times
some steps in your post that you say "then"
i can't understand how you got them
and how i go further to proove my inequality

can you please wright me the solution to this problem
??
 
  • #4
No, I can't!
 

FAQ: A question in prooving function convergence

What is function convergence?

Function convergence refers to the behavior of a sequence of functions as the independent variable approaches a certain value or limit. In simpler terms, it is the tendency of a function to approach a specific value as its input values get closer and closer to a particular value.

How is function convergence proven?

Function convergence is typically proven using the epsilon-delta definition, which states that a function f(x) converges to a limit L as x approaches c if, for any positive number ε, there exists a corresponding positive number δ such that |f(x) - L| < ε whenever 0 < |x - c| < δ.

What is the importance of proving function convergence?

Proving function convergence is important in many areas of mathematics and science. It allows us to understand the behavior of a function and make predictions about its value at certain points. It also helps us establish the existence of a limit for a given function, which is crucial in many mathematical proofs and applications.

What are some common techniques used to prove function convergence?

Some common techniques used to prove function convergence include the squeeze theorem, the monotone convergence theorem, and the Cauchy criterion. These techniques involve manipulating the properties of a function to show that it approaches a specific value as its input values get closer to a certain point or limit.

Can a function converge to more than one limit?

No, a function can only converge to one limit. This is because the definition of function convergence requires that the function approaches a specific value as its input values get closer to a certain point. If a function were to have multiple limits, it would violate this definition and would not be considered convergent.

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