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Ch. 3 - Derivatives
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Non è quello che usi tu?Cambia libro di testo
Capitolo 3, Problema 3.8.89

A challenging second derivative Find d²y/dx², where √y+xy=1.

Guida verificata passo dopo passo
1
Start by differentiating the given equation \( \sqrt{y} + xy = 1 \) with respect to \( x \). Use implicit differentiation since \( y \) is a function of \( x \).
Differentiate \( \sqrt{y} \) with respect to \( x \). This requires the chain rule: \( \frac{d}{dx}(\sqrt{y}) = \frac{1}{2\sqrt{y}} \cdot \frac{dy}{dx} \).
Differentiate \( xy \) with respect to \( x \). Use the product rule: \( \frac{d}{dx}(xy) = x \cdot \frac{dy}{dx} + y \cdot 1 \).
Set the derivative of the left side equal to the derivative of the right side (which is 0) to form the first derivative equation: \( \frac{1}{2\sqrt{y}} \cdot \frac{dy}{dx} + x \cdot \frac{dy}{dx} + y = 0 \). Solve for \( \frac{dy}{dx} \).
Differentiate the expression for \( \frac{dy}{dx} \) with respect to \( x \) to find \( \frac{d^2y}{dx^2} \). Use implicit differentiation again, applying the product rule and chain rule as necessary.

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Implicit Differentiation

Implicit differentiation is a technique used to differentiate equations where the dependent variable is not isolated on one side. In this case, we have the equation √y + xy = 1, which involves both x and y. By differentiating both sides with respect to x, we can find dy/dx and subsequently d²y/dx².
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Percorso guidato
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Finding The Implicit Derivative

Second Derivative

The second derivative, denoted as d²y/dx², measures the rate of change of the first derivative (dy/dx) with respect to x. It provides information about the concavity of the function and can indicate points of inflection. To find the second derivative, we differentiate the first derivative again, applying the rules of differentiation appropriately.
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The Second Derivative Test: Finding Local Extrema

Chain Rule

The chain rule is a fundamental principle in calculus used to differentiate composite functions. When differentiating an expression involving y, which is a function of x, we apply the chain rule to account for the relationship between x and y. This is crucial when finding dy/dx and d²y/dx² in implicit differentiation scenarios.
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Intro to the Chain Rule