Chapter 13: Problem 26
Find \(d y / d x\) by implicit differentiation. $$ x^{2 / 3}+y^{2 / 3}=2 $$
Short Answer
Expert verified
\(\frac{dy}{dx} = -\left(\frac{x}{y}\right)^{-1/3}\).
Step by step solution
01
Understand the problem and define implicit differentiation
The given equation \(x^{2/3} + y^{2/3} = 2\) involves both \(x\) and \(y\). We are tasked with finding \(\frac{dy}{dx}\), the derivative of \(y\) with respect to \(x\), using implicit differentiation. This technique is required because \(y\) is not isolated.
02
Differentiate with respect to x
Differentiate each term of the equation \(x^{2/3} + y^{2/3} = 2\) with respect to \(x\). Using the power rule, the derivative of the first term is \(\frac{2}{3}x^{-1/3}\). For the second term, apply the chain rule to find \(\frac{2}{3}y^{-1/3} \frac{dy}{dx}\). Differentiating the right side, the constant 2 yields 0.
03
Set up the implicit differentiation equation
Combine the derivatives from Step 2 to create the equation: \(\frac{2}{3}x^{-1/3} + \frac{2}{3}y^{-1/3} \frac{dy}{dx} = 0\).
04
Solve for dy/dx
Isolate \(\frac{dy}{dx}\) by first moving the \(\frac{2}{3}x^{-1/3}\) term to the right side, resulting in \(\frac{2}{3}y^{-1/3} \frac{dy}{dx} = -\frac{2}{3}x^{-1/3}\). Divide both sides by \(\frac{2}{3}y^{-1/3}\) to get \(\frac{dy}{dx} = -\frac{x^{-1/3}}{y^{-1/3}}\).
05
Simplify the expression for dy/dx
Simplify the right side to obtain \(\frac{dy}{dx} = -\left(\frac{x}{y}\right)^{-1/3}\). This is the implicit derivative of \(y\) with respect to \(x\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Derivatives
In calculus, derivatives are a fundamental tool for understanding how functions change. When we say \( \ \frac{dy}{dx} \ \), we mean the rate of change of the variable \ \ y \ \ with respect to the variable \ \ x \ \. Essentially, it tells us how \ \ y \ \ behaves when \ \ x \ \ changes infinitesimally.
- In explicit functions like \ \ y = f(x) \ \, finding derivatives is straightforward because \ \ y \ \ is isolated.
- Implicit differentiation is necessary when \ \ y \ \ is intermixed with \ \ x \ \ within an equation, such as \ \ x^{2/3} + y^{2/3} = 2 \ \.
Chain Rule
The chain rule is an essential principle in calculus when differentiating compositions of functions. It states that if a variable \( y \) is dependent on another variable \( u \), which in turn depends on \( x \), then the derivative of \( y \) with respect to \( x \) is the derivative of \( y \) with respect to \( u \) times the derivative of \( u \) with respect to \( x \):\[ \frac{dy}{dx} = \frac{dy}{du} \times \frac{du}{dx} \].
- In our implicit differentiation example, the term \( y^{2/3} \) needs the chain rule because \( y \) itself is a function of \( x \).
- Therefore, its derivative with respect to \( x \) becomes \( \frac{2}{3}y^{-1/3} \cdot \frac{dy}{dx} \).
Power Rule
The power rule provides a simple way to differentiate functions of the form \( x^n \). It states that if \( f(x) = x^n \), then the derivative \( f'(x) = nx^{n-1} \). This rule makes taking derivatives straightforward when dealing with polynomial expressions. In our problem, both \( x^{2/3} \) and \( y^{2/3} \) required differentiation.
- The derivative of \( x^{2/3} \) using the power rule is \ \frac{2}{3}x^{-1/3} \ \.
- For \( y^{2/3} \), the power rule applies within the context of the chain rule.
Calculus
Calculus is the branch of mathematics that studies how things change. It is a powerful framework for solving a wide range of problems involving rates of change and the accumulation of quantities. The exercise demonstrates crucial calculus tools: derivatives, the chain rule, and the power rule.
- **Derivatives** measure the rate at which one quantity changes with respect to another.
- **The chain rule** helps articulate the relationship of composite functions when differentiating.
- **The power rule** simplifies the process of finding derivatives for polynomial expressions.