How Do You Prove a Limit Using the ε-δ Definition?

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Homework Help Overview

The discussion revolves around using the ε-δ definition of limits to prove that the limit of the function (2x - 6)/(x - 3) as x approaches 3 equals 2. Participants are exploring the necessary steps and reasoning involved in this proof.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to simplify the expression and questions whether their simplification leads to a proof of the limit. Other participants inquire about the reduction of the expression and clarify the requirements for a formal proof.

Discussion Status

Participants are actively engaging with the original poster's reasoning and providing guidance on the necessary steps to complete the proof. There is a focus on ensuring that all conditions of the ε-δ definition are satisfied, with some participants questioning the completeness of the original poster's approach.

Contextual Notes

There is an emphasis on the need for a formal proof, and participants are discussing the implications of the simplification process and the conditions under which the limit can be considered proven.

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Homework Statement



Use the ε-δ definition of the limit to prove that

lim as x -> 3 of (2x - 6)/(x-3) = 2

Homework Equations



The Attempt at a Solution



I've started a preliminary analysis for the proof:
For any ε>0, find δ=δ(ε) such that 0 < |x - 3| < δ implies that |(2x - 6)/(x-3) - 2|< ε.
Simplifying:
|(2x - 6)/(x-3) - 2| = |(2x - 6 - 2(x - 3))/(x-3)| = |(2x - 6 - 2x + 6)/(x - 3)| = 0

Where do I go from here? Have I just proven that since the simplified form is 0, which is less than ε, and therefore proven the limit?
 
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What do you get when you reduce (2x-6)/(x-3) to lowest terms?
 
2. Does that mean I've proved the limit? No formal proof required?
 
No. Any δ > 0 will work, but you still need to show that for any x such that 0 < |x - 3| [STRIKE]< δ[/STRIKE] , |(2x - 6)/(x-3) - 2|< ε .

I crossed out the < δ side, because as long as (x-3) ≠ 0, (2x - 6)/(x-3) - 2 = 0 which, of course is less than ε .
 

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