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Ch. 4 - Applications of the Derivative
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Non è quello che usi tu?Cambia libro di testo
Capitolo 4, Problema 4.R.116a

Cosine limits Let n be a positive integer. Evaluate the following limits.




lim_x→0 (1 - cos xⁿ) / x²ⁿ

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Recognize that the limit involves an indeterminate form 0/0 as x approaches 0, which suggests the use of L'Hôpital's Rule or a series expansion.
Consider using the Taylor series expansion for cos(x) around x = 0: cos(x) ≈ 1 - x²/2 + x⁴/24 - ... . For cos(xⁿ), substitute xⁿ into the series: cos(xⁿ) ≈ 1 - (xⁿ)²/2 + (xⁿ)⁴/24 - ... .
Substitute the series expansion into the limit expression: (1 - (1 - (xⁿ)²/2 + ...)) / x²ⁿ = ((xⁿ)²/2 - ...) / x²ⁿ.
Simplify the expression: ((x²ⁿ)/2 - ...) / x²ⁿ = (1/2) - ... . As x approaches 0, higher order terms become negligible.
Conclude that the limit evaluates to 1/2 as x approaches 0, since the dominant term in the expansion is (1/2).

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In calculus, the limit of a function describes the behavior of that function as its input approaches a certain value. It is a fundamental concept used to define continuity, derivatives, and integrals. Evaluating limits often involves techniques such as substitution, factoring, or applying L'Hôpital's rule when dealing with indeterminate forms.
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