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Ch. 3 - Derivatives
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Not the one you use?Change textbook
Chapter 3, Problem 3.8.58a

58–59. Carry out the following steps.
a. Use implicit differentiation to find dy/dx.
xy^5/2+x^3/2y=12; (4, 1)

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1
Start by differentiating both sides of the equation with respect to x. Remember that y is a function of x, so you'll need to use implicit differentiation. The equation is: \( xy^{\frac{5}{2}} + x^{\frac{3}{2}}y = 12 \).
Apply the product rule to the term \( xy^{\frac{5}{2}} \). The product rule states that \( \frac{d}{dx}[u \cdot v] = u'v + uv' \). Here, let \( u = x \) and \( v = y^{\frac{5}{2}} \). Differentiate each part: \( u' = 1 \) and \( v' = \frac{5}{2}y^{\frac{3}{2}} \cdot \frac{dy}{dx} \).
Differentiate the second term \( x^{\frac{3}{2}}y \) using the product rule again. Let \( u = x^{\frac{3}{2}} \) and \( v = y \). Differentiate each part: \( u' = \frac{3}{2}x^{\frac{1}{2}} \) and \( v' = \frac{dy}{dx} \).
Combine the results from the differentiation steps. You will have an equation involving \( \frac{dy}{dx} \). Collect all terms involving \( \frac{dy}{dx} \) on one side of the equation and factor out \( \frac{dy}{dx} \).
Solve for \( \frac{dy}{dx} \) by isolating it on one side of the equation. Substitute the point (4, 1) into the equation to find the specific value of \( \frac{dy}{dx} \) at that point.

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Key Concepts

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

Implicit Differentiation

Implicit differentiation is a technique used to differentiate equations where the dependent and independent variables are not isolated on one side. Instead of solving for y explicitly, we differentiate both sides of the equation with respect to x, applying the chain rule when necessary. This method is particularly useful for equations that are difficult or impossible to rearrange.
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Finding The Implicit Derivative

Chain Rule

The chain rule is a fundamental principle in calculus that allows us to differentiate composite functions. It states that if a function y is defined as a function of u, which in turn is a function of x, then the derivative of y with respect to x can be found by multiplying the derivative of y with respect to u by the derivative of u with respect to x. This is essential in implicit differentiation when dealing with terms involving y.
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Evaluating Derivatives at a Point

After finding the derivative dy/dx using implicit differentiation, it is often necessary to evaluate this derivative at a specific point, such as (4, 1) in this case. This involves substituting the x and y values into the derived expression to find the slope of the tangent line at that point. This step is crucial for understanding the behavior of the function at specific coordinates.
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