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Ch. 7 - Transcendental Functions
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Not the one you use?Change textbook
Chapter 7, Problem 7.PE.21

In Exercises 1–24, find the derivative of y with respect to the appropriate variable.
21. y = z arcsec(z) - √(z² - 1), z>1

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1
Identify the function to differentiate: \(y = z \cdot \operatorname{arcsec}(z) - \sqrt{z^{2} - 1}\), where \(z > 1\).
Recall the derivative of \(\operatorname{arcsec}(z)\) with respect to \(z\): \(\frac{d}{dz} \operatorname{arcsec}(z) = \frac{1}{|z| \sqrt{z^{2} - 1}}\). Since \(z > 1\), \(|z| = z\).
Apply the product rule to the first term \(z \cdot \operatorname{arcsec}(z)\): \(\frac{d}{dz} [z \cdot \operatorname{arcsec}(z)] = \operatorname{arcsec}(z) \cdot \frac{d}{dz} z + z \cdot \frac{d}{dz} \operatorname{arcsec}(z)\).
Differentiate the second term \(- \sqrt{z^{2} - 1}\) using the chain rule: rewrite as \(-(z^{2} - 1)^{1/2}\) and find its derivative.
Combine the derivatives from the product rule and the chain rule to write the full expression for \(\frac{dy}{dz}\).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Derivative of Inverse Trigonometric Functions

Inverse trigonometric functions like arcsec(x) have specific derivative formulas. For arcsec(x), the derivative is 1 / (|x|√(x² - 1)) when |x| > 1. Understanding this formula is essential to differentiate expressions involving arcsec.
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Derivatives of Other Inverse Trigonometric Functions

Product Rule for Differentiation

The product rule is used to differentiate products of two functions. If y = u(x)v(x), then y' = u'v + uv'. Applying this rule correctly is crucial when differentiating terms like z * arcsec(z).
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Chain Rule and Differentiation of Composite Functions

The chain rule helps differentiate composite functions, such as √(z² - 1). It states that the derivative of f(g(x)) is f'(g(x)) * g'(x). This rule is necessary to handle the square root of an expression involving z.
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