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Evaluating a Limit In Exercises \(15-42\) , evaluate the limit, using L'Hopital's Rule if necessary. $$\lim _{x \rightarrow 1} \frac{x^{11}-1}{x^{4}-1}$4

Short Answer

Expert verified
The evaluated limit is \( \frac{11}{4} \)

Step by step solution

01

Identify Indeterminate Form

Firstly, substitute x=1 into the expression to check if the limit form is 0/0 or infinity/infinity which are indeterminate forms. If so, we're able to apply L'Hopital's Rule. \[ \lim _{x \rightarrow 1} \frac{{x^{11}-1}}{{x^{4}-1}} = \frac{{1^{11}-1}}{{1^{4}-1}} = \frac{0}{0} \] So this is of the form 0/0, an indeterminate form.
02

Apply L'Hopital's Rule

Since we have the indeterminate form 0/0, we can apply L'Hopital's Rule. This rule states that the limit of a ratio of two functions as x approaches a certain value is equal to the limit of their derivatives. So take the derivative of the numerator and the denominator: \( \lim _{x \rightarrow 1} \frac{{11*x^{10}}}{{4*x^{3}}} \)
03

Reevaluate the limit

Now substitute x=1 into the new expression \[ \lim _{x \rightarrow 1} \frac{{11*x^{10}}}{{4*x^{3}}} = \frac{{11*1^{10}}}{{4*1^{3}}} = \frac{11}{4} \]
04

The Final Limit

So, \( \lim _{x \rightarrow 1} \frac{{x^{11}-1}}{{x^{4}-1}} = \frac{11}{4} \)

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Key Concepts

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

L'Hopital's Rule
Understanding L'Hopital's Rule is crucial when you're dealing with the evaluation of limits, especially when those limits result in indeterminate forms. When you substitute a value into an expression and get a form like 0/0 or \(\infty/\infty\), that's when L'Hopital's Rule comes into play.

The rule says, put simply, if you find an indeterminate form \( \frac{0}{0} \) or \( \frac{\infty}{\infty} \), you can take the derivatives of both the numerator and the denominator separately and then evaluate the limit. It can sometimes take several applications if the indeterminate form persists after the first application. But remember, L'Hopital's Rule can only be used when these specific conditions are met.

In the exercise mentioned, we apply L'Hopital's Rule because the limit \( \lim _{x \rightarrow 1} \frac{x^{11}-1}{x^{4}-1} \) resulted in the indeterminate form 0/0. The derivatives of the numerator \(11x^{10}\) and the denominator \(4x^{3}\) are then used to find the limit, which in this case simplifies to \(\frac{11}{4}\) when \(x\) approaches 1.
Indeterminate Forms
Indeterminate forms occur when evaluating a limit leads to an expression that doesn’t initially offer a clear value. The most common indeterminate forms are 0/0, \(\infty/\infty\), \(0\cdot\infty\), \(\infty - \infty\), \(0^0\), \(\infty^0\), and \(1^\infty\).

It's important to recognize these because they signal that additional work is needed to find the limit's value, often by using methods such as algebraic simplification, factoring, conjugation, or applying L'Hopital's Rule. In our textbook problem, the form 0/0 indicated the need for L'Hopital's Rule to find the accurate limit as \(x\) approaches 1.

Understanding indeterminate forms can help you determine the best approach to solving a limit problem and when it’s appropriate to use tools like L'Hopital’s Rule, which we did in our exercise example to achieve the solution.
Derivatives
Derivatives are a fundamental concept in calculus that represent the rate at which a function is changing at any given point. They are essential when applying L'Hopital's Rule for finding the limit of a function that yields an indeterminate form.

The derivative of a function at a particular point can be thought of as the slope of the tangent to the function's graph at that point. For the function \(f(x) = x^n\), the derivative is \(f'(x) = nx^{n-1}\) which follows the power rule, one of the basic rules of differentiation.

When we encounter limits like those in the exercise, identifying and calculating the derivatives correctly is key. In our step-by-step solution, correctly finding the derivative of the numerator, \(11x^{10}\), and the denominator, \(4x^{3}\), and then evaluating the limit allowed us to solve what appeared to be a complex limit with ease, arriving at the final answer of \(\frac{11}{4}\).

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