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Ch. 7 - Transcendental Functions
Hass - Thomas' Calculus 15th Edition
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7장, 문제 7.PE.88

Use l’Hôpital’s Rule to find the limits in Exercises 85–108.
88. lim(x→0) (tan x)/(x + sin(x))

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First, identify the form of the limit as \( x \to 0 \). Substitute \( x = 0 \) into the expression \( \frac{\tan x}{x + \sin x} \) to check if it results in an indeterminate form.
Since \( \tan 0 = 0 \), \( 0 + \sin 0 = 0 \), the limit is of the form \( \frac{0}{0} \), which is indeterminate and allows the use of l’Hôpital’s Rule.
Apply l’Hôpital’s Rule by differentiating the numerator and denominator separately with respect to \( x \). The derivative of the numerator \( \tan x \) is \( \sec^2 x \).
The derivative of the denominator \( x + \sin x \) is \( 1 + \cos x \).
Rewrite the limit as \( \lim_{x \to 0} \frac{\sec^2 x}{1 + \cos x} \) and then evaluate this new limit by substituting \( x = 0 \).

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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

Limit of a Function as x Approaches a Point

The limit describes the value that a function approaches as the input approaches a specific point. Understanding how to evaluate limits, especially when direct substitution leads to indeterminate forms, is essential for applying techniques like l’Hôpital’s Rule.
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Limits of Rational Functions: Denominator = 0

Derivatives of Trigonometric Functions

Knowing the derivatives of trigonometric functions such as tan(x) and sin(x) is crucial when applying l’Hôpital’s Rule. For example, the derivative of tan(x) is sec²(x), and the derivative of sin(x) is cos(x), which are used to find the new limit after differentiation.
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Derivatives of Other Inverse Trigonometric Functions