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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 7.6.21

In Exercises 21–48, find the derivative of y with respect to the appropriate variable.
21. y=arccos(x²)

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Identify the function given: \(y = \arccos(x^{2})\). We want to find \(\frac{dy}{dx}\), the derivative of \(y\) with respect to \(x\).
Recall the derivative formula for the inverse cosine function: \(\frac{d}{dx}[\arccos(u)] = -\frac{1}{\sqrt{1 - u^{2}}} \cdot \frac{du}{dx}\), where \(u\) is a function of \(x\).
In this problem, set \(u = x^{2}\). Then compute \(\frac{du}{dx} = 2x\).
Substitute \(u = x^{2}\) and \(\frac{du}{dx} = 2x\) into the derivative formula to get: \(\frac{dy}{dx} = -\frac{1}{\sqrt{1 - (x^{2})^{2}}} \cdot 2x\).
Simplify the expression inside the square root: \((x^{2})^{2} = x^{4}\), so the derivative becomes \(\frac{dy}{dx} = -\frac{2x}{\sqrt{1 - x^{4}}}\).

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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 arccos(x) have specific derivative formulas. For arccos(x), the derivative is -1 divided by the square root of (1 - x²). Understanding this formula is essential to differentiate expressions involving arccos.
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Derivatives of Other Inverse Trigonometric Functions

Chain Rule

The chain rule is used to differentiate composite functions. When a function is composed of an outer function and an inner function, 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

Power Rule

The power rule states that the derivative of xⁿ is n times x raised to the (n-1) power. This rule is necessary to differentiate the inner function x² in the given problem.
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