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Ch. 7 - Transcendental Functions
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Non è quello che usi tu?Cambia libro di testo
Capitolo 7, Problema 7.7.37b

Verify the integration formulas in Exercises 37–40.
37. b. ∫sech(x)dx = sin⁻¹(tanh x) + C

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Recall the definition of the hyperbolic secant function: \(\text{sech}(x) = \frac{1}{\cosh(x)}\) and the hyperbolic tangent function: \(\tanh(x) = \frac{\sinh(x)}{\cosh(x)}\).
Set up the integral to verify: \(\int \text{sech}(x) \, dx\) and consider the substitution \(u = \tanh(x)\), since the derivative of \(\tanh(x)\) is related to \(\text{sech}^2(x)\).
Compute the derivative of \(u\): \(\frac{du}{dx} = \text{sech}^2(x)\), which suggests expressing \(\text{sech}(x)\) in terms of \(u\) and \(du\) might require manipulation.
Rewrite \(\text{sech}(x)\) as \(\frac{\text{sech}^2(x)}{\text{sech}(x)}\) and use the substitution \(u = \tanh(x)\) to express the integral in terms of \(u\) and \(du\).
Recognize that the integral transforms into \(\int \frac{1}{\sqrt{1 - u^2}} \, du\), which corresponds to the inverse sine function, leading to the result \(\sin^{-1}(\tanh(x)) + C\).

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