1. **State the problem:** Given the equation $$xy + 7x - 8x^2 = 5$$, we need to find the derivative $y'$ by implicit differentiation and then solve for $y$ explicitly and differentiate to find $y'$ again.
2. **Implicit differentiation:** Differentiate both sides with respect to $x$. Use the product rule for $xy$:
$$\frac{d}{dx}(xy) + \frac{d}{dx}(7x) - \frac{d}{dx}(8x^2) = \frac{d}{dx}(5)$$
3. Applying the product rule to $xy$:
$$x \frac{dy}{dx} + y \frac{dx}{dx} + 7 - 16x = 0$$
which is
$$x y' + y + 7 - 16x = 0$$
4. Solve for $y'$:
$$x y' = 16x - 7 - y$$
$$y' = \frac{16x - 7 - y}{x}$$
5. **Solve for $y$ explicitly:**
$$xy + 7x - 8x^2 = 5$$
$$xy = 5 - 7x + 8x^2$$
$$y = \frac{5 - 7x + 8x^2}{x}$$
6. Simplify $y$:
$$y = \frac{5}{x} - 7 + 8x$$
7. **Differentiate $y$ explicitly:**
$$y' = \frac{d}{dx}\left(\frac{5}{x} - 7 + 8x\right) = -\frac{5}{x^2} + 0 + 8 = 8 - \frac{5}{x^2}$$
8. **Check consistency:** Substitute $y$ from step 6 into the implicit derivative formula from step 4:
$$y' = \frac{16x - 7 - \left(\frac{5}{x} - 7 + 8x\right)}{x} = \frac{16x - 7 - \frac{5}{x} + 7 - 8x}{x} = \frac{8x - \frac{5}{x}}{x} = \frac{8x^2 - 5}{x^2} = 8 - \frac{5}{x^2}$$
This matches the explicit derivative.
**Final answers:**
(a) $$y' = \frac{16x - 7 - y}{x}$$
(b) $$y' = 8 - \frac{5}{x^2}$$
Implicit Differentiation 86C372
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