Implicit Differentiation 4Cf987
1. **State the problem:** Given the implicit equation $$x + xy - 2x^3 = 2$$, we need to find \(\frac{dy}{dx}\) by implicit differentiation (part a), solve for \(y\) as a function of \(x\) and find \(\frac{dy}{dx}\) explicitly (part b), and confirm the consistency of both derivatives by expressing the implicit derivative as a function of \(x\) alone (part c).
2. **Part (a): Differentiate implicitly**
- Differentiate both sides with respect to \(x\):
$$\frac{d}{dx}(x) + \frac{d}{dx}(xy) - \frac{d}{dx}(2x^3) = \frac{d}{dx}(2)$$
- Using the product rule on \(xy\):
$$1 + \left(x \frac{dy}{dx} + y \right) - 6x^2 = 0$$
- Rearranged:
$$1 + x \frac{dy}{dx} + y - 6x^2 = 0$$
- Solve for \(\frac{dy}{dx}\):
$$x \frac{dy}{dx} = 6x^2 - y - 1$$
$$\frac{dy}{dx} = \frac{6x^2 - y - 1}{x}$$
3. **Part (b): Solve for \(y\) explicitly and find \(\frac{dy}{dx}\)**
- From the original equation:
$$x + xy - 2x^3 = 2$$
- Isolate \(y\):
$$xy = 2 + 2x^3 - x$$
$$y = \frac{2 + 2x^3 - x}{x} = \frac{2}{x} + 2x^2 - 1$$
- Differentiate \(y\) with respect to \(x\):
$$\frac{dy}{dx} = -\frac{2}{x^2} + 4x$$
4. **Part (c): Confirm consistency by expressing implicit derivative as function of \(x\) only**
- Substitute \(y = \frac{2}{x} + 2x^2 - 1\) into the implicit derivative:
$$\frac{dy}{dx} = \frac{6x^2 - \left(\frac{2}{x} + 2x^2 - 1\right) - 1}{x}$$
- Simplify numerator:
$$6x^2 - \frac{2}{x} - 2x^2 + 1 - 1 = 4x^2 - \frac{2}{x}$$
- So:
$$\frac{dy}{dx} = \frac{4x^2 - \frac{2}{x}}{x} = \frac{4x^2}{x} - \frac{2}{x \cdot x} = 4x - \frac{2}{x^2}$$
- This matches the explicit derivative found in part (b).
**Final answer:**
$$\frac{dy}{dx} = 4x - \frac{2}{x^2}$$