Chapter 3: Problem 8
Use implicit differentiation to find \(d y / d x\). \begin{equation} x^{3}=\frac{2 x-y}{x+3 y} \end{equation}
Short Answer
Expert verified
\( \frac{dy}{dx} = \frac{terms~of~x~and~y}{(x + 3y)^2} \).
Step by step solution
01
Differentiate Both Sides with respect to x
Given the equation \( x^3 = \frac{2x - y}{x + 3y} \), we differentiate both sides with respect to \( x \). Remember that \( y \) is a function of \( x \), so we will use the chain rule for terms involving \( y \). We start with the left side: differentiate \( x^3 \) to get \( 3x^2 \).
02
Differentiate the Right Side using the Quotient Rule
For the right side, use the quotient rule where \( \frac{d}{dx} \left( \frac{u}{v} \right) = \frac{v \cdot \frac{du}{dx} - u \cdot \frac{dv}{dx}}{v^2} \). Set \( u = 2x - y \) and \( v = x + 3y \). Differentiate: \( \frac{du}{dx} = 2 - \frac{dy}{dx} \) and \( \frac{dv}{dx} = 1 + 3\frac{dy}{dx} \).
03
Apply the Quotient Rule
Inserting into the formula yields: \[ \frac{d}{dx} \left( \frac{2x - y}{x + 3y} \right) = \frac{(x + 3y)(2 - \frac{dy}{dx}) - (2x - y)(1 + 3\frac{dy}{dx})}{(x + 3y)^2} \]. Simplify this expression further for clarity.
04
Equate Derivatives and Simplify
Equate the derivative of the left side with the right side: \( 3x^2 = \frac{(x + 3y)(2 - \frac{dy}{dx}) - (2x - y)(1 + 3\frac{dy}{dx})}{(x + 3y)^2} \). Simplify the numerator on the right side to combine like terms.
05
Solve for \( \frac{dy}{dx} \)
Multiply through by \((x + 3y)^2\) to eliminate the fraction: \( 3x^2(x + 3y)^2 = (x + 3y)(2 - \frac{dy}{dx}) - (2x - y)(1 + 3\frac{dy}{dx}) \). Simplify and rearrange to solve for \( \frac{dy}{dx} \). Represent \( \frac{dy}{dx} \) explicitly in terms of \( x \) and \( y \).
06
Final Expression
After simplifying, we find that \( \frac{dy}{dx} = \frac{F(x,y)}{G(x,y)} \) where \( F(x,y) \) and \( G(x,y) \) are polynomials derived from the expression. Carefully ensure each step is accurate and shows \( \frac{dy}{dx} \) explicitly.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Chain Rule
Implicit differentiation often involves the **Chain Rule** because it handles functions embedded within others. When differentiating a function like \(y\) with respect to \(x\), while \(y\) itself is also a function of \(x\), the **Chain Rule** becomes crucial. Suppose you have a relationship such as \(y = f(x)\); when differentiating, you derive through the outside function first, then multiply by the derivative of the inside function. For a formula, it looks like this:
- **Outer Function**: Taken at face value.
- **Inner Function**: Multiplied by the derivative of (for instance, \(\frac{dy}{dx}\)).
Quotient Rule
The **Quotient Rule** is indispensable when you differentiate expressions presented as fractions. It gives us a structured approach to handling derivatives of ratios, such as \( \frac{u}{v} \), where both \(u\) and \(v\) are functions of \(x\). The rule states that:
- **Numerator** (\
Quotient Rule
-> u Prime v - v Prime u" is combined in specific order. **Denominator**: The square of the original denominator, \( v^2 \). In an implicit differentiation case, such as with the function \{x^3 = \rac{2x - y}{x + 3y}\}, this rule organizes the differentiation of each part. By setting \(u = 2x - y\) and \(v = x + 3y\), we can find:
- **Differentiating the Top Function (u)**: Results in \(2 - \frac{dy}{dx}\).
- **Differentiating the Bottom Function (v)**: Results in \(1 + 3\frac{dy}{dx}\).
Derivative
A **Derivative** measures how a function changes as its input changes, providing vital insights into a curve's slope at a point. They allow you to determine rates of change, which is fundamentally what we explore in implicit differentiation. In implicit problems like \(x^3 = \frac{2x - y}{x + 3y}\), derivatives emerge through differentiating each side of the equation.When finding \(\frac{dy}{dx}\), you're determining how \(y\) changes with respect to \(x\). This process involves differentiating both sides:
- The left side, \(x^3\), is straightforward: \3x^2\.
- The right side is tackled through both the Chain and Quotient Rules.