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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 7.7.29

In Exercises 25–36, find the derivative of y with respect to the appropriate variable.
29. y = (1 - t)coth⁻¹(√t)

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1
Identify the function given: \(y = (1 - t) \, \text{coth}^{-1}(\sqrt{t})\). We need to find \(\frac{dy}{dt}\), the derivative of \(y\) with respect to \(t\).
Recognize that \(y\) is a product of two functions of \(t\): \(u = (1 - t)\) and \(v = \text{coth}^{-1}(\sqrt{t})\). Use the product rule for differentiation: \(\frac{dy}{dt} = u'v + uv'\).
Compute \(u' = \frac{d}{dt}(1 - t) = -1\).
Find \(v' = \frac{d}{dt} \left( \text{coth}^{-1}(\sqrt{t}) \right)\). Use the chain rule: first find the derivative of \(\text{coth}^{-1}(x)\) with respect to \(x\), then multiply by the derivative of \(\sqrt{t}\) with respect to \(t\).
Recall that \(\frac{d}{dx} \text{coth}^{-1}(x) = -\frac{1}{1 - x^2}\) for \(|x| > 1\). Then, \(\frac{d}{dt} \sqrt{t} = \frac{1}{2\sqrt{t}}\). Combine these to find \(v' = -\frac{1}{1 - (\sqrt{t})^2} \cdot \frac{1}{2\sqrt{t}} = -\frac{1}{1 - t} \cdot \frac{1}{2\sqrt{t}}\).
Substitute \(u\), \(u'\), \(v\), and \(v'\) back into the product rule formula to express \(\frac{dy}{dt} = (-1) \cdot \text{coth}^{-1}(\sqrt{t}) + (1 - t) \cdot \left(-\frac{1}{1 - t} \cdot \frac{1}{2\sqrt{t}}\right)\). Simplify the expression as much as possible.

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Key Concepts

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

Inverse Hyperbolic Cotangent Function (coth⁻¹)

The inverse hyperbolic cotangent function, coth⁻¹(x), is the inverse of the hyperbolic cotangent. It can be expressed in terms of logarithms and is defined for |x| > 1. Understanding its domain and derivative formula is essential for differentiating expressions involving coth⁻¹.
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Derivatives of Other Inverse Trigonometric Functions

Chain Rule

The chain rule is a fundamental differentiation technique used when dealing with composite functions. It states that the derivative of a composite function is the derivative of the outer function evaluated at the inner function times the derivative of the inner function. This is crucial when differentiating functions like coth⁻¹(√t).
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Intro to the Chain Rule

Product Rule

The product rule is used to differentiate products of two functions. It states that the derivative of f(t)g(t) is f'(t)g(t) + f(t)g'(t). Since y is given as a product of (1 - t) and coth⁻¹(√t), applying the product rule correctly is necessary to find dy/dt.
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The Product Rule