Chapter 3: Problem 72
Exponential Limit Evaluate: \(\lim _{x \rightarrow 0}\left(\frac{e^{x^{3}}-1-x^{3}}{\sin ^{6} 2 x}\right)\)
Short Answer
Expert verified
The limit as x approaches 0 of \(\frac{e^{x^{3}}-1-x^{3}}{\sin ^{6} 2x}\) is 0.
Step by step solution
01
Inspecting the Limit Form
We first plug in 0 into the expression. After substitution, \(e^{0^{3}}-1-0^{3}\) evaluates to 0, and \(\sin^{6} (2*0)\) also evaluates to 0. This confirms the limit is in the form 0/0, hence we can apply L'Hopital's rule.
02
Applying L'Hopital's Rule
We are going to differentiate the numerator and the denominator until we get a limit that we can evaluate without getting 0/0. Let's start applying L'Hopital's rule: \(\lim _{x \rightarrow 0}\left(\frac{e^{x^{3}}-1-x^{3}}{\sin ^{6} 2x}\right) = \lim _{x \rightarrow 0}\left(\frac{3xe^{x^{3}}-3x^{2}}{6 \sin ^{5}2x (2\cos(2x))}\right)\). If we substitute x=0 into this new expression, we still get a 0/0 form. So, we apply L'Hopital's rule again to get: \(\lim _{x \rightarrow 0}\left(\frac{3e^{x^{3}}-3x^{2}}{6 \sin ^{5}2x (2\cos(2x))}\right) = \lim _{x \rightarrow 0}\left(\frac{3x^{2}e^{x^{3}}-6x}{-24 \sin ^{4}2x \cos(2x) -12 \sin ^{5}2x \sin(2x)}\right)\)
03
Evaluate the Limit
After differentiating it twice, we have managed to get an evaluation that is not in the 0/0 form. When x=0, the numerator is equal to 0 and the denominator is non-zero, so the limit evaluates to 0.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
L'Hopital's Rule
L'Hopital's Rule is a powerful tool in calculus used to evaluate limits that result in indeterminate forms such as \( \frac{0}{0} \) or \( \frac{\infty}{\infty} \). It states that if the limit \( \lim_{x \to a} \frac{f(x)}{g(x)} \) results in these forms, we can differentiate the numerator \( f(x) \) and the denominator \( g(x) \) and then take the limit again:
- Differentiate the numerator, \( f'(x) \)
- Differentiate the denominator, \( g'(x) \)
- Re-evaluate the limit, \( \lim_{x \to a} \frac{f'(x)}{g'(x)} \)
Limit Evaluation
Limit evaluation involves determining the value that a function approaches as the input approaches a particular point. It is foundational in calculus, offering insights into the behavior of functions near specific values. To evaluate a limit:
- Substitute the value into the function, unless it causes division by zero or another undefined expression.
- If direct substitution results in an indeterminate form, use techniques like factoring, conjugates, or L'Hopital's Rule to simplify.
Differentiation
Differentiation is the mathematical procedure of finding the derivative of a function. A derivative represents the function's rate of change and is fundamental to calculus. When faced with solving a limit problem using L'Hopital's Rule, differentiation becomes crucial:
- Derivative of exponential functions like \( e^{x^3} \) involves the chain rule.
- Trigonometric functions require specific rules, like the derivative of \( \sin(x) \) being \( \cos(x) \).
Trigonometric Limits
Trigonometric limits are calculations involving trigonometric functions as the variable approaches a particular value. For instance, common forms like \( \lim_{x \to 0} \frac{\sin(x)}{x} = 1 \) serve as critical benchmarks. When dealing with trigonometric expressions:
- Use identities such as \( \sin(2x) = 2 \sin(x)\cos(x) \) to simplify expressions.
- Recognize standard limits to ease complex trigonometric limit problems.
- Apply L'Hopital's Rule to transform the indeterminate forms \( \frac{0}{0} \) involving trigonometric functions into solvable forms.