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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 7.7.13

In Exercises 13–24, find the derivative of y with respect to the appropriate variable.
13. y = 6sinh(x/3)

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Recall the definition of the hyperbolic sine function: \(\sinh(u)\), where \(u\) is a function of \(x\). The derivative of \(\sinh(u)\) with respect to \(x\) is \(\cosh(u) \cdot \frac{du}{dx}\).
Identify the inner function \(u = \frac{x}{3}\). We will need to find \(\frac{du}{dx}\).
Calculate the derivative of the inner function: \(\frac{du}{dx} = \frac{d}{dx} \left( \frac{x}{3} \right) = \frac{1}{3}\).
Apply the chain rule to differentiate \(y = 6 \sinh \left( \frac{x}{3} \right)\): \(\frac{dy}{dx} = 6 \cdot \cosh \left( \frac{x}{3} \right) \cdot \frac{1}{3}\).
Simplify the expression for the derivative: \(\frac{dy}{dx} = 2 \cosh \left( \frac{x}{3} \right)\).

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Key Concepts

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

Hyperbolic Sine Function (sinh)

The hyperbolic sine function, sinh(x), is defined as (e^x - e^(-x))/2. It is similar to the sine function but relates to hyperbolic geometry. Understanding its definition helps in differentiating expressions involving sinh.
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Graph of Sine and Cosine Function

Chain Rule

The chain rule is a differentiation technique used when a function is composed of another function, such as y = f(g(x)). It states that 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

Derivative of Hyperbolic Functions

The derivative of sinh(x) with respect to x is cosh(x), the hyperbolic cosine function. Knowing this derivative is essential for differentiating expressions involving sinh, especially when combined with the chain rule.
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Asymptotes of Hyperbolas