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Use implicit differentiation and the product rule 2. Find \( \frac{d y}{d x} \) implicitly for the following functions: \[ \text { a. } f(x)=x^{2}+2 x y^{4}=-2 \] \[ \begin{array}{l}\text { b. } \\ \qquad \begin{array}{l}4 \\ 4\end{array} \\ \qquad x^{5}=2 x^{3}\end{array} \]

Ask by Cole Page. in the United States
Mar 11,2025

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For part a: \[ \frac{dy}{dx} = \frac{-(x + y^{4})}{4xy^{3}} \] For part b: \[ x = 0, \quad x = \sqrt{\frac{6}{5}}, \quad x = -\sqrt{\frac{6}{5}} \]

Solution

To find \( \frac{d y}{d x} \) implicitly for the given functions, we will apply implicit differentiation and the product rule where necessary. ### Part a: Given the equation: \[ f(x) = x^{2} + 2xy^{4} = -2 \] 1. **Differentiate both sides with respect to \( x \)**: \[ \frac{d}{dx}(x^{2}) + \frac{d}{dx}(2xy^{4}) = \frac{d}{dx}(-2) \] 2. **Differentiate each term**: - The derivative of \( x^{2} \) is \( 2x \). - For \( 2xy^{4} \), we use the product rule: \[ \frac{d}{dx}(2xy^{4}) = 2\left( y^{4} \frac{d}{dx}(x) + x \frac{d}{dx}(y^{4}) \right) = 2\left( y^{4} + x \cdot 4y^{3} \frac{dy}{dx} \right) \] - The derivative of a constant \(-2\) is \(0\). 3. **Combine the derivatives**: \[ 2x + 2\left( y^{4} + 4xy^{3} \frac{dy}{dx} \right) = 0 \] 4. **Simplify**: \[ 2x + 2y^{4} + 8xy^{3} \frac{dy}{dx} = 0 \] 5. **Isolate \( \frac{dy}{dx} \)**: \[ 8xy^{3} \frac{dy}{dx} = -2x - 2y^{4} \] \[ \frac{dy}{dx} = \frac{-2x - 2y^{4}}{8xy^{3}} = \frac{-(x + y^{4})}{4xy^{3}} \] ### Part b: Given the equation: \[ x^{5} = 2x^{3} \] 1. **Rearrange the equation**: \[ x^{5} - 2x^{3} = 0 \] 2. **Differentiate both sides with respect to \( x \)**: \[ \frac{d}{dx}(x^{5}) - \frac{d}{dx}(2x^{3}) = 0 \] 3. **Differentiate each term**: - The derivative of \( x^{5} \) is \( 5x^{4} \). - The derivative of \( 2x^{3} \) is \( 6x^{2} \). 4. **Combine the derivatives**: \[ 5x^{4} - 6x^{2} = 0 \] 5. **Factor out common terms**: \[ x^{2}(5x^{2} - 6) = 0 \] 6. **Set each factor to zero**: - \( x^{2} = 0 \) gives \( x = 0 \). - \( 5x^{2} - 6 = 0 \) gives \( x^{2} = \frac{6}{5} \) or \( x = \pm \sqrt{\frac{6}{5}} \). Since there is no \( y \) term in this equation, we do not find \( \frac{dy}{dx} \) explicitly for part b, as it is not an implicit function of \( y \). ### Summary of Results: - For part a: \[ \frac{dy}{dx} = \frac{-(x + y^{4})}{4xy^{3}} \] - For part b, the solutions for \( x \) are: \[ x = 0, \quad x = \sqrt{\frac{6}{5}}, \quad x = -\sqrt{\frac{6}{5}} \]

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The Deep Dive

To find \( \frac{d y}{d x} \) implicitly for the given functions, we need to apply implicit differentiation and, in the case of \( f(x)=x^{2}+2 x y^{4}=-2 \), the product rule. For \( f(x) = x^2 + 2xy^4 = -2 \): 1. Differentiate both sides with respect to \( x \): \[ \frac{d}{dx}(x^2) + \frac{d}{dx}(2xy^4) = \frac{d}{dx}(-2) \] This gives \( 2x + 2\left( y^4 + x \cdot 4y^3 \frac{dy}{dx} \right) = 0 \). 2. Rearranging this, we have: \[ 2x + 2y^4 + 8xy^3 \frac{dy}{dx} = 0 \] Solving for \( \frac{dy}{dx} \): \[ 8xy^3 \frac{dy}{dx} = -2x - 2y^4 \] \[ \frac{dy}{dx} = \frac{-2x - 2y^4}{8xy^3} = \frac{-x - y^4}{4xy^3} \] For \( x^5 = 2x^3 \): 1. Differentiate both sides with respect to \( x \): \[ \frac{d}{dx}(x^5) = \frac{d}{dx}(2x^3) \] This gives \( 5x^4 = 6x^2 \frac{dy}{dx} \). 2. Rearranging gives: \[ \frac{dy}{dx} = \frac{5x^4}{6x^2} = \frac{5x^2}{6} \] Thus, we have: - For (a): \( \frac{dy}{dx} = \frac{-x - y^4}{4xy^3} \) - For (b): \( \frac{dy}{dx} = \frac{5x^2}{6} \)

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