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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 7.7.23

In Exercises 13–24, find the derivative of y with respect to the appropriate variable.
23. y = (x²+1)sech(ln x)
(Hint: Before differentiating, express in terms of exponentials and simplify.)

Guida verificata passo dopo passo
1
Recognize that the function is a product of two functions: \(y = (x^{2} + 1) \cdot \text{sech}(\ln x)\). We will need to use the product rule for differentiation, which states: \(\frac{d}{dx}[u \cdot v] = u'v + uv'\).
Rewrite the hyperbolic secant function in terms of exponentials. Recall that \(\text{sech}(z) = \frac{2}{e^{z} + e^{-z}}\). So, \(\text{sech}(\ln x) = \frac{2}{e^{\ln x} + e^{-\ln x}}\).
Simplify the expression inside the denominator using properties of logarithms and exponentials: \(e^{\ln x} = x\) and \(e^{-\ln x} = \frac{1}{x}\). Thus, \(\text{sech}(\ln x) = \frac{2}{x + \frac{1}{x}}\).
Simplify the denominator further by combining terms: \(x + \frac{1}{x} = \frac{x^{2} + 1}{x}\). Therefore, \(\text{sech}(\ln x) = \frac{2}{\frac{x^{2} + 1}{x}} = \frac{2x}{x^{2} + 1}\).
Rewrite the original function using this simplification: \(y = (x^{2} + 1) \cdot \frac{2x}{x^{2} + 1}\). Notice that \((x^{2} + 1)\) cancels out, so \(y = 2x\). Now, differentiate \(y = 2x\) with respect to \(x\) using basic differentiation rules.

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Hyperbolic Secant Function and Its Exponential Form

The hyperbolic secant function, sech(x), can be expressed using exponentials as sech(x) = 2 / (e^x + e^(-x)). This form simplifies differentiation by converting hyperbolic functions into exponential terms, making it easier to apply derivative rules.
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Chain Rule

The chain rule is used to differentiate composite functions. When a function is nested inside another, such as sech(ln x), the derivative is the derivative of the outer function evaluated at the inner function times the derivative of the inner function.
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Intro to the Chain Rule

Product Rule

The product rule is applied when differentiating the product of two functions, like (x² + 1) and sech(ln x). It states that the derivative is the first function times the derivative of the second plus the second function times the derivative of the first.
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The Product Rule