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Squeeze Theorem

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The Squeeze Theorem (also called the Sandwich Theorem or the Squeeze Play Theorem) is a relatively simple theorem that deals with calculus, specifically limits.

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Squeeze Theorem

Contents

Theorem

Suppose is between and for all in a neighborhood of the point . If and approach some common limit as approaches , then .

Proof

If is between and for all in the neighborhood of , then either or for all in this neighborhood. The two cases are the same up to renaming our functions, so assume without loss of generality that .

We must show that for all there is some for which implies .

Now since \lim_{x\to S}g(x)=\lim_{x\to S}h(x)=L, there must exist such that

|x-S|<\delta_1 \Rightarrow |g(x)-L|<\varepsilon \textrm{  and  } |x-S|<\delta_2 \Rightarrow |h(x)-L|<\varepsilon.

Now let \delta = \min\{\delta_1,\delta_2\}. If then

-\varepsilon < g(x) - L \leq f(x) - L \leq h(x) - L < \varepsilon.

So . Now by the definition of a limit we get as desired.

Applications and examples

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See Also

Want to learn how to tackle those tough AMC/AIME/Olympiad counting and probability problems? Check out Art of Problem Solving's NEW Intermediate Counting & Probability by David Patrick.
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