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In Problems 39-56, use the limit laws to evaluate each limit. $$ \lim _{x \rightarrow 2} \frac{2-x}{x^{2}-4} $$

Short Answer

Expert verified
The limit is \( \frac{-1}{4} \).

Step by step solution

01

Identify the form of the limit expression

First, substitute the value of 2 into the expression to check if it's in an indeterminate form. Substitute 2 into the numerator and denominator: \( 2 - 2 = 0 \) and \( 2^2 - 4 = 4 - 4 = 0 \). The limit is in the form \( \frac{0}{0} \), so we must simplify the expression.
02

Factor the denominator

The denominator \( x^2 - 4 \) is a difference of squares and can be factored. Write \( x^2 - 4 \) as \( (x-2)(x+2) \). Now the limit expression becomes \( \lim_{x \to 2} \frac{2-x}{(x-2)(x+2)} \).
03

Simplify the expression

Notice that the numerator \( 2-x \) can be rewritten as \( -(x-2) \). The limit expression can then be written as \( \lim_{x \to 2} \frac{-(x-2)}{(x-2)(x+2)} \).
04

Cancel the common terms

Cancel the \( (x-2) \) terms in the numerator and denominator of the expression. The expression now simplifies to \( \lim_{x \to 2} \frac{-1}{x+2} \).
05

Evaluate the limit

Now substitute \( x = 2 \) in the simplified expression. This gives \( \frac{-1}{2+2} = \frac{-1}{4} \). The limit is \( \frac{-1}{4} \).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Indeterminate Forms
Indeterminate forms occur when evaluating a mathematical limit results in expressions like \( \frac{0}{0} \), \( \frac{\infty}{\infty} \), or other ambiguous forms, which don't provide clear information about the limit's behavior. In the original problem, when we substitute \( x = 2 \) into the limit \( \lim _{x \rightarrow 2} \frac{2-x}{x^{2}-4} \), the result is \( \frac{0}{0} \), an indeterminate form. This means we cannot directly evaluate the limit by simple substitution. Instead, we need to manipulate the expression to find the limit.Often, resolving an indeterminate form requires algebraic manipulation, like factoring or rationalizing. The goal is to transform the limit expression into a form where direct substitution becomes possible, as seen in the steps where \( x^2 - 4 \) was factored without changing the limit's value.
Limit Laws
Limit laws are fundamental tools that help us evaluate limits by breaking them down into more manageable parts. These laws include the sum, difference, product, and quotient laws for limits, and they provide a framework for understanding how limits behave in various contexts.When evaluating the limit \( \lim _{x \rightarrow 2} \frac{2-x}{x^{2}-4} \) after simplifying it, we reached a point where we could apply these laws. For example, by factoring and canceling terms, we simplified the expression significantly. This left us with \( \lim_{x \to 2} \frac{-1}{x+2} \), a straightforward expression where we can directly substitute \( x = 2 \) to find the limit equals \( \frac{-1}{4} \).Using limit laws allows substitution after every possible algebraic manipulation alleviates indeterminate forms, reconciling them to a simple evaluation.
Factoring Polynomials
Factoring polynomials involves rewriting a polynomial as a product of its factors, which can reveal more about its structure and simplify expressions for easier manipulation and evaluation. In the original exercise, the polynomial in the denominator, \( x^2 - 4 \), is a difference of squares, a specific type of polynomial which can be easily factored into \( (x-2)(x+2) \).Once we factor \( x^2-4 \), the potential for simplifying or cancelling terms in the overall fraction is revealed. This step is crucial when dealing with limits involving polynomials, especially when confronting indeterminate forms like \( \frac{0}{0} \). Factoring not only simplifies the solving process but also ensures accuracy in reaching the final value of the limit, allowing us to apply the limit laws effectively.Recognizing patterns, like the difference of squares, is key in efficiently factoring polynomials—a necessary skill in algebra and calculus.

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