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Ch. 7 - Transcendental Functions
Hass - Thomas' Calculus 15th Edition
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7장, 문제 7.5.22

Use l’Hôpital’s rule to find the limits in Exercises 7–52.


22. lim (x → 1) (x - 1) / (ln x - sin πx)

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First, verify that the limit is an indeterminate form of type \( \frac{0}{0} \) or \( \frac{\infty}{\infty} \) by substituting \( x = 1 \) into the expression \( \frac{x - 1}{\ln x - \sin \pi x} \).
Since direct substitution gives \( \frac{0}{0} \), apply l'Hôpital's Rule, which states that \( \lim_{x \to a} \frac{f(x)}{g(x)} = \lim_{x \to a} \frac{f'(x)}{g'(x)} \) if the original limit is an indeterminate form.
Find the derivative of the numerator: \( f(x) = x - 1 \), so \( f'(x) = 1 \).
Find the derivative of the denominator: \( g(x) = \ln x - \sin \pi x \). Use the derivatives \( \frac{d}{dx} \ln x = \frac{1}{x} \) and \( \frac{d}{dx} \sin \pi x = \pi \cos \pi x \), so \( g'(x) = \frac{1}{x} - \pi \cos \pi x \).
Evaluate the new limit \( \lim_{x \to 1} \frac{f'(x)}{g'(x)} = \lim_{x \to 1} \frac{1}{\frac{1}{x} - \pi \cos \pi x} \) by substituting \( x = 1 \).

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

l’Hôpital’s Rule

l’Hôpital’s Rule is a method for evaluating limits that result in indeterminate forms like 0/0 or ∞/∞. It states that the limit of a ratio of functions can be found by taking the limit of the ratio of their derivatives, provided certain conditions are met.
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Power Rules

Limits Involving Logarithmic and Trigonometric Functions

Understanding how logarithmic functions (like ln x) and trigonometric functions (like sin πx) behave near specific points is crucial. This helps in simplifying expressions and determining if direct substitution leads to indeterminate forms.
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Introduction to Trigonometric Functions

Derivative Computation

Calculating derivatives of functions such as (x - 1), ln x, and sin πx accurately is essential when applying l’Hôpital’s Rule. Knowing the derivative rules for polynomials, logarithms, and trigonometric functions ensures correct application of the rule.
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