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Use implicit differentiation to find \(d y / d x\). \begin{equation} (3 x y+7)^{2}=6 y \end{equation}

Short Answer

Expert verified
\(\frac{dy}{dx} = \frac{-y(3xy + 7)}{x(3xy + 7) - 1}\)

Step by step solution

01

Differentiate both sides implicitly with respect to x

First, differentiate the left-hand side of the equation using the chain rule. The derivative of \((3xy + 7)^2\) is \(2(3xy + 7)\) times the derivative of \(3xy + 7\), which is \(3y + 3x \frac{dy}{dx}\). For the right-hand side, differentiate \(6y\) to get \(6 \frac{dy}{dx}\). This gives us the equation:\[2(3xy + 7)(3y + 3x \frac{dy}{dx}) = 6 \frac{dy}{dx}\]
02

Simplify and rearrange

Distribute the \(2(3xy + 7)\) through the terms \(3y + 3x \frac{dy}{dx}\):\[6y(3xy + 7) + 6x(3xy + 7) \frac{dy}{dx} = 6 \frac{dy}{dx}\].Rearrange the equation to isolate the terms containing \(\frac{dy}{dx}\) on one side:\[6x(3xy + 7) \frac{dy}{dx} - 6 \frac{dy}{dx} = -6y(3xy + 7)\].
03

Factor out \(\frac{dy}{dx}\) and solve

Factor \(\frac{dy}{dx}\) from the left-hand side:\[(6x(3xy + 7) - 6) \frac{dy}{dx} = -6y(3xy + 7)\].Divide both sides by \((6x(3xy + 7) - 6)\) to solve for \(\frac{dy}{dx}\):\[\frac{dy}{dx} = \frac{-6y(3xy + 7)}{6x(3xy + 7) - 6}\].
04

Simplify the expression for \(\frac{dy}{dx}\)

Notice that you can factor out a 6 from the numerator and denominator:\[\frac{dy}{dx} = \frac{-y(3xy + 7)}{x(3xy + 7) - 1}\].This is the simplified form of the derivative.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Chain Rule
The Chain Rule is a fundamental tool in calculus for differentiating compositions of functions. The basic idea is to take the derivative of the outer function with respect to the inner function, and then multiply it by the derivative of the inner function. This concept is especially important when dealing with complex expressions like \((3xy + 7)^2\) in implicit differentiation.

For this exercise, we apply the Chain Rule to the expression on the left side of the equation. First, we identify \((3xy + 7)^2\) as the outer function and \(3xy + 7\) as the inner function.
  • The derivative of the outer function \((u^2)\) is \(2u\).
  • The derivative of the inner function \(3xy + 7\) involves applying the product rule for \(3xy\) and then adding the derivative of 7, which is 0.
  • Since \(3xy\) is a product of \(3x\) and \(y\), its derivative is \(3y + 3x \frac{dy}{dx}\), where \(\frac{dy}{dx}\) is the derivative of \(y\) with respect to \(x\).
Putting it all together gives \[2(3xy + 7)(3y + 3x \frac{dy}{dx})\]. This shows us how the Chain Rule helps to break down complicated functions into manageable parts.
Partial Derivatives
Partial derivatives come into play when functions have more than one variable, as is often the case in implicit differentiation problems.

In this exercise, we differentiate a function that involves both \(x\) and \(y\), which requires us to find the derivative indirectly with respect to \(x\).

To find \(\frac{dy}{dx}\), we differentiate every term involving \(y\) partially with respect to \(x\), treating \(y\) not as a constant but as a function dependent on \(x\). This requires applying the Chain Rule to terms like \(3xy\):
  • The term \(3xy\) is seen as a product of \(3x\) and \(y\). Here, \(x\) is a variable, and \(y\) is a function of \(x\).
  • A differentiation approach is used, adding the Chain Rule component to account for both variables.
  • This yields terms like \(3y\) and \(3x\frac{dy}{dx}\), clearly showing the influence of both \(x\) and \(y\) in the derivative calculation.
By managing these partial derivatives carefully, we solve the differential equation step-by-step, ultimately finding the implicit derivative.
Calculus Problem Solving
Solving calculus problems, particularly those involving implicit differentiation, requires a blend of strategic thinking and mathematical technique.

In this exercise, the goal is to find \(\frac{dy}{dx}\), the derivative of \(y\) with respect to \(x\).

Here are some key steps:
  • Differentiate Both Sides: Start by differentiating both sides of the equation to express \(\frac{dy}{dx}\) in terms of known quantities.
  • Simplify and Rearrange: Collect all terms involving \(\frac{dy}{dx}\) on one side. This step often requires algebraic manipulation like distributing and factoring.
  • Factor and Solve: Isolate \(\frac{dy}{dx}\) by factoring it out of the left-hand side of the equation. Then, solve for it by division.
Ensuring each of these steps is done methodically is key. For instance, in our solution, isolating \(\frac{dy}{dx}\) required careful arrangement and factoring, after which we could divide across the equation to solve for the derivative.

Integrating these strategies helps to handle complex calculus problems effectively, providing a clear pathway to the solution.

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Most popular questions from this chapter

Suppose that the functions \(f\) and \(g\) and their derivatives with respect to \(x\) have the following values at \(x=0\) and \(x=1 .\) $$\begin{array}{|c|c|c|c|}\hline x & {f(x)} & {g(x)} & {f^{\prime}(x)} & {g^{\prime}(x)} \\ \hline 0 & {1} & {1} & {5} & {1 / 3} \\ \hline 1 & {3} & {-4} & {-1 / 3} & {-8 / 3} \\ \hline\end{array}$$ Find the derivatives with respect to \(x\) of the following combinations at the given value of \(x .\) $$\begin{array}{ll}{\text { a. } 5 f(x)-g(x),} & {x=1 \quad \text { b. } f(x) g^{3}(x), \quad x=0} \\ {\text { c. } \frac{f(x)}{g(x)+1}, \quad x=1} & {\text { d. } f(g(x)), \quad x=0}\end{array}$$ $$\begin{array}{l}{\text { e. } g(f(x)), \quad x=0 \quad \text { f. }\left(x^{11}+f(x)\right)^{-2}, \quad x=1} \\ {\text { g. } f(x+g(x)), \quad x=0}\end{array}$$

Use a CAS to perform the following steps. \begin{equation} \begin{array}{l}{\text { a. Plot the equation with the implicit plotter of a CAS. Check to }} \\ {\text { see that the given point } P \text { satisfies the equation. }} \\ {\text { b. Using implicit differentiation, find a formula for the deriva- }} \\ {\text { tive } d y / d x \text { and evaluate it at the given point } P .}\end{array} \end{equation} \begin{equation} \begin{array}{l}{\text { c. Use the slope found in part (b) to find an equation for the tan- }} \\ {\text { gent line to the curve at } P \text { . Then plot the implicit curve and }} \\ {\text { tangent line together on a single graph. }}\end{array} \end{equation} \begin{equation} x \sqrt{1+2 y}+y=x^{2}, \quad P(1,0) \end{equation}

Particle motion The position of a particle moving along a coordinate line is \(s=\sqrt{1+4 t},\) with \(s\) in meters and \(t\) in seconds. Find the particle's velocity and acceleration at \(t=6 \mathrm{sec}\) .

Diagonals If \(x, y,\) and \(z\) are lengths of the edges of a rectangular box, the common length of the box's diagonals is \(s=\) \(\sqrt{x^{2}+y^{2}+z^{2}}\) a. Assuming that \(x, y,\) and \(z\) are differentiable functions of \(t\) how is \(d s / d t\) related to \(d x / d t, d y / d t,\) and \(d z / d t\) ? b. How is \(d s / d t\) related to \(d y / d t\) and \(d z / d t\) if \(x\) is constant? c. How are \(d x / d t, d y / d t,\) and \(d z / d t\) related if \(s\) is constant?

If \(x^{2}+y^{2}=25\) and \(d x / d t=-2,\) then what is \(d y / d t\) when \(x=3\) and \(y=-4 ?\)

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