Chapter 7: Problem 38
Use implicit differentiation to find \(y^{\prime}\). $$ y^{3}+x^{2} \ln y=5 x+3 $$
Short Answer
Expert verified
\(y' = \frac{5 - 2x \ln y}{3y^2 + \frac{x^2}{y}}\).
Step by step solution
01
Differentiate Both Sides
Differentiate both sides of the equation with respect to \(x\). Remember that \(y\) is a function of \(x\), so you will need to apply the chain rule. The differentiation will look like this: \[ \frac{d}{dx}(y^3) + \frac{d}{dx}(x^2 \ln y) = \frac{d}{dx}(5x + 3). \]
02
Differentiate Terms
For the first term \(y^3\), use the chain rule: \[ \frac{d}{dx}(y^3) = 3y^2 \cdot y'. \] For the second term \(x^2 \ln y\), apply the product rule:\[ \frac{d}{dx}(x^2 \ln y) = \frac{d}{dx}(x^2) \cdot \ln y + x^2 \cdot \frac{d}{dx}(\ln y) = 2x \ln y + x^2 \cdot \frac{1}{y} \cdot y'. \]The third term, on the right side, is simplified as:\[ \frac{d}{dx}(5x + 3) = 5. \]
03
Combine the Differentiated Terms
Now substitute the differentiated terms back into the equation:\[ 3y^2 \cdot y' + 2x \ln y + x^2 \cdot \frac{1}{y} \cdot y' = 5. \]
04
Solve for \(y'\)
Combine the terms that contain \(y'\) to isolate it:\[ y'(3y^2 + \frac{x^2}{y}) = 5 - 2x \ln y. \]Finally, solve for \(y'\):\[ y' = \frac{5 - 2x \ln y}{3y^2 + \frac{x^2}{y}}. \]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Chain Rule
Understanding the chain rule is a vital part of implicit differentiation. This rule helps us differentiate compositions of functions smoothly. When we have a function like \(y = g(x)\), where \(y\) is a function of \(x\), using the chain rule allows us to differentiate expressions where \(y\) isn’t isolated. In our exercise, when differentiating \(y^3\), you apply the chain rule by taking the derivative of the outer function first and then the inner function.
- Start by differentiating the outer part: \(y^3\), which becomes \(3y^2\).
- Then multiply by the derivative of the inner function \(y\) with respect to \(x\), which is \(y'\).
Product Rule
The product rule is the go-to rule for differentiating terms that are products of two functions. In our scenario, we handle the term \(x^2 \ln y\) using the product rule. The product rule states that for two functions \(f(x)\) and \(g(x)\), the derivative of their product is:\[ (f(x)g(x))' = f'(x)g(x) + f(x)g'(x). \]For \(x^2 \ln y\), look at it as a product of two functions: \(f(x) = x^2\) and \(g(x) = \ln y\).
- Differentiating \(f(x) = x^2\) gives \(2x\).
- Keep \(g(x)\) as it is: \(\ln y\).
- Differentiating \(g(x) = \ln y\) gives \(\frac{1}{y}\cdot y'\), by the chain rule since \(y\) is a function of \(x\).
- Combine them: \(2x \ln y + x^2 \cdot \frac{1}{y} \cdot y'\).
Derivative
At the heart of calculus lies the concept of derivatives. A derivative tells us both the rate at which a function changes and the direction of that change. When we perform implicit differentiation, we are essentially finding the derivative, \(y'\), of a function that isn't in standard form, i.e., \(y = f(x)\).
- Start differentiating all terms concerning \(x\), which in this exercise means recognizing \(y\) as a function of \(x\).
- Use established techniques like the chain and product rules effectively to handle different types of terms like polynomials or products of functions.
- Recollect that any constant has a derivative of zero, simplifying rightmost terms like \(5x + 3\) directly to \(5\).
- Combine and rearrange the derivatives to find \(y'\).