Chapter 2: Problem 12
Find dy/dx by implicit differentiation. $$ \left(2 x^{2}+3 y^{2}\right)^{5 / 2}=x $$
Short Answer
Expert verified
The short answer is: \(\frac{dy}{dx} = \frac{1 - \frac{5}{2}(2x^2+3y^2)^{3/2}}{6y}\).
Step by step solution
01
Differentiate both sides of the equation with respect to x
Start by differentiating both sides of the equation \(\left(2 x^{2}+3 y^{2}\right)^{5 / 2}=x\) concerning x.
We will apply the Chain Rule on the left side, which states that if the function defined as \(u = g(x)\) and \(y = f(u)\), then the derivative of y with respect to x is:
\(\frac{dy}{dx} = f'(u) \cdot g'(x)\)
Let's differentiate the left side of the equation first.
Let \(u = 2x^2 + 3y^2\), and the left side is a function of u, so \(y = u^{5/2}\).
02
Differentiate both sides concerning u
Now, let's differentiate both sides concerning u: \(y = u^{5/2}\).
\(\frac{dy}{du} = \frac{5}{2}u^{(5/2)-1} = \frac{5}{2}u^{3/2}\)
Now, find the derivative of u with respect to x: \(u = 2x^2 + 3y^2\).
\(\frac{du}{dx} = 4x + 6y\frac{dy}{dx}\)
03
Chain Rule to differentiate left side of the equation concerning x
Now we will apply the Chain Rule to differentiate the left side of the original equation concerning x:
\(\frac{dy}{dx} = \frac{dy}{du} \cdot \frac{du}{dx}\)
Substitute \(\frac{dy}{du} = \frac{5}{2}u^{3/2}\) and \(\frac{du}{dx} = 4x + 6y\frac{dy}{dx}\):
\(\frac{dy}{dx} = \frac{5}{2}u^{3/2}(4x + 6y\frac{dy}{dx})\)
Since \(u = 2x^2 + 3y^2\), substitute for u:
\(\frac{dy}{dx} = \frac{5}{2}(2x^2+3y^2)^{3/2}(4x +6y\frac{dy}{dx})\)
Now, differentiate the right side of the original equation concerning x:
\(\frac{d}{dx}(x) = 1\)
04
Solve for dy/dx
Now, we have two equations:
1) \(\frac{dy}{dx} = \frac{5}{2}(2x^2+3y^2)^{3/2}(4x +6y\frac{dy}{dx})\)
2) \(\frac{d}{dx}(x) = 1\)
Set the two equations equal to each other (since both equations are the derivative of the original equation):
\( \frac{5}{2}(2x^2+3y^2)^{3/2}(4x+6y\frac{dy}{dx}) = 1\)
Now, solve for \(\frac{dy}{dx}\):
\(\frac{dy}{dx}\left(\frac{5}{2}(2x^2+3y^2)^{3/2}(4x +6y\frac{dy}{dx})\right) = 1(4x + 6y\frac{dy}{dx})\)
\(5(2x^2+3y^2)^{3/2} = 2(4x + 6y\frac{dy}{dx})\)
Divide both sides by 2:
\(\frac{5}{2}(2x^2+3y^2)^{3/2} = 4x + 6y\frac{dy}{dx}\)
Subtract \(4x\) from both sides:
\(6y\frac{dy}{dx} = 1 - \frac{5}{2}(2x^2+3y^2)^{3/2}\)
Finally, divide by \(6y\) to isolate \(\frac{dy}{dx}\):
\(\frac{dy}{dx} = \frac{1 - \frac{5}{2}(2x^2+3y^2)^{3/2}}{6y}\)
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Chain Rule Explained
Implicit differentiation often involves the use of a handy tool in calculus known as the Chain Rule. It's particularly useful for differentiating composite functions. This rule allows us to differentiate a function based on another function. Suppose you have a composition of two functions, where one function, say \(u\), is a function of \(x\), and another, say \(y\), is a function of \(u\). The Chain Rule states that:
Don't forget: implicit differentiation can involve multiple layers of chain applications, especially when dealing with equations where \(y\) is not isolated.
- If \(y = f(u)\) and \(u = g(x)\), then \(\frac{dy}{dx} = \frac{dy}{du} \cdot \frac{du}{dx}\).
Don't forget: implicit differentiation can involve multiple layers of chain applications, especially when dealing with equations where \(y\) is not isolated.
Understanding Derivatives
Derivatives are central to calculus, acting as a tool to measure the rate at which a quantity changes. In the context of implicit differentiation, we deal with functions that are intertwined, where one variable is a function of another.
To differentiate implicitly means we take the derivative with respect to one variable, treating other variables as functions themselves. When you face a term like \(3y^2\), where \(y\) is a variable depending on \(x\), the derivative becomes more complex than straightforward differentiation:
To differentiate implicitly means we take the derivative with respect to one variable, treating other variables as functions themselves. When you face a term like \(3y^2\), where \(y\) is a variable depending on \(x\), the derivative becomes more complex than straightforward differentiation:
- The derivative of \(3y^2\) with respect to \(x\) is \(6y\frac{dy}{dx}\), because \(y\) itself depends on \(x\).
- The appearance of \(\frac{dy}{dx}\) signals a dependency that one variable has on another.
Tackling Calculus Problem Solving: Implicit Differentiation
Calculus problem solving can seem tricky, but with a structured approach, it becomes more manageable. With implicit differentiation, problems often involve differentiating both sides of an equation where the dependent variable is entangled with the independent one.
Here’s a breakdown for tackling these problems:
Here’s a breakdown for tackling these problems:
- Identify the functions: Determine which parts of your equation are composite, requiring the Chain Rule for differentiation.
- Differentiation Process: Start by differentiating each term on both sides with respect to \(x\). For terms involving \(y\), remember to multiply by \(\frac{dy}{dx}\), since \(y\) is implicitly a function of \(x\).
- Combine & Solve: Once differentiated, combine terms logically. Solving for \(\frac{dy}{dx}\) might involve isolating terms and rearranging the equation.
- Check accuracy: Re-evaluate each derivative step to ensure constants and expressions are correctly derived.