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Use l'Hopital's rule to find the limits in Exercises \(7-50\) $$\lim _{x \rightarrow-5} \frac{x^{2}-25}{x+5}$$

Short Answer

Expert verified
The limit is -10.

Step by step solution

01

Identify the Form

First, we substitute \( x = -5 \) into the given function \( rac{x^2-25}{x+5} \) to check the limit form. This results in \( \frac{(-5)^2-25}{-5+5} = \frac{25-25}{0} = \frac{0}{0} \), which is an indeterminate form.
02

Apply L'Hopital's Rule

L'Hopital's Rule can be applied when a limit evaluates to an indeterminate form like \( \frac{0}{0} \). The rule states to take the derivative of the numerator and the denominator separately. For the function \( \frac{x^2-25}{x+5} \), the derivative of the numerator, \( x^2-25 \), is \( 2x \), and the derivative of the denominator, \( x+5 \), is \( 1 \). Therefore, the limit can be re-evaluated as \( \lim_{x \to -5} \frac{2x}{1} \).
03

Compute the New Limit

Substitute \( x = -5 \) into the new expression obtained by using L'Hopital's Rule: \( \lim_{x \to -5} \frac{2x}{1} = 2(-5) = -10 \). Therefore, the limit is \( -10 \).

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Key Concepts

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

Indeterminate Forms
When dealing with limits, sometimes substituting the value directly into a function results in an expression that is undefined or unclear. These are known as indeterminate forms. A common type of indeterminate form is \(\frac{0}{0}\). This form occurs, as demonstrated in the given exercise when substituting \(x = -5\) into the function \(\frac{x^2-25}{x+5}\) results in \(\frac{0}{0}\), which does not provide a clear limit.Understanding indeterminate forms is crucial because they signal that the limit cannot be resolved through simple substitution. Other indeterminate forms include \(\frac{\infty}{\infty}\), \(\infty - \infty\), and \(0 \times \infty\). Recognizing these forms allows us to apply special techniques, like L'Hopital's Rule, to solve limits that initially appear insoluble.
Derivatives
Derivatives are a fundamental concept in calculus, representing the rate at which a function changes at any point. They provide the slope of the tangent line to the curve of the function.In the context of L'Hopital's Rule, derivatives play a key role when evaluating limits that result in indeterminate forms. By taking the derivative of the numerator and the numerator separately, we form a new function that often resolves the indeterminacy. For instance, with the function \(\frac{x^2-25}{x+5}\), the derivative of the numerator \(x^2 - 25\) is \(2x\), while the derivative of the denominator \(x+5\) is \(1\). This transforms the original function and provides a new way to evaluate the limit that bypasses the indeterminate form.
Limit Evaluation
Evaluating limits often involves determining the value that a function approaches as the input approaches a certain point. There are different strategies depending on the function's behavior.The use of L'Hopital's Rule is particular to when evaluating limits that result in indeterminate forms like \(\frac{0}{0}\). Once the appropriate derivatives are taken, as seen with \(\frac{2x}{1}\) from the earlier example, the limit becomes straightforward to evaluate by direct substitution. Substituting \(x = -5\) gives \(2(-5) = -10\). This is the value the original function approaches as \(x\) nears \(-5\).Ultimately, limit evaluation using L'Hopital’s Rule helps simplify the process and reach a conclusive value, which might otherwise remain elusive due to initial indeterminate forms.

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