# Multivariable Limits, Squeeze Principle

1. Sep 18, 2012

### dr721

1. The problem statement, all variables and given/known data

(Squeeze Principle) Suppose f, g, and h are real-valued functions on a neighborhood of a (perhaps not including the point a itself). Suppose f(x) ≤ g(x) ≤ h(x) for all x and limx→a f(x) = l = limx→a h(x). Prove that limx→a g(x) = l. (Hint: Given ε > 0, show that there is δ > 0 so that whenever 0 < ||x - a|| < δ, we have -ε < f(x) - lg(x) - lh(x) - l < ε.)

2. The attempt at a solution

I don't understand the definition of a limit with ε and δ. The question confuses me, frankly, and I don't have any idea where I would begin. Could anyone help me understand this?

2. Sep 19, 2012

### voko

There are two equivalent definitions of the limit, in terms of sequences and in terms of epsilon-delta. Both can be used to prove the squeeze principle.

What is your difficulty with the epsilon-delta definition?

3. Sep 19, 2012

### dr721

I guess I don't actually understand what epsilon and delta mean. Like, I'm struggling to understand how they define the limit.

4. Sep 19, 2012

### voko

Do you understand how the limit is defined in the 1D case?

5. Sep 19, 2012

### dr721

Actually, I don't know that specific definition at all. My calculus teacher spent very little time doing limits. We learned the basic skill of taking a limit and L'Hopital's Rule, and then went straight into derivatives.

I know a limit is a way of looking at the continuity/discontinuity of a function, but that's about it.

6. Sep 19, 2012