Implicit Differentiation 8A1501
1. **Problem:** Evaluate $\frac{dy}{dx}$ when $1 + xy^2 + x^2y = 0$.
2. **Formula and rules:** Use implicit differentiation. Differentiate both sides of the equation with respect to $x$. Remember to use the product rule: $\frac{d}{dx}[uv] = u'v + uv'$.
3. Differentiate each term:
- $\frac{d}{dx}[1] = 0$
- $\frac{d}{dx}[xy^2] = y^2 + x \cdot 2y \frac{dy}{dx} = y^2 + 2xy \frac{dy}{dx}$
- $\frac{d}{dx}[x^2y] = 2xy + x^2 \frac{dy}{dx}$
4. Substitute into the differentiated equation:
$$0 + y^2 + 2xy \frac{dy}{dx} + 2xy + x^2 \frac{dy}{dx} = 0$$
5. Group terms with $\frac{dy}{dx}$ and without:
$$y^2 + 2xy + (2xy + x^2) \frac{dy}{dx} = 0$$
6. Isolate $\frac{dy}{dx}$:
$$ (2xy + x^2) \frac{dy}{dx} = - (y^2 + 2xy) $$
7. Solve for $\frac{dy}{dx}$:
$$ \frac{dy}{dx} = \frac{-(y^2 + 2xy)}{2xy + x^2} = \frac{-y(y + 2x)}{x(2y + x)} $$
8. Note that $x(2y + x) = x(x + 2y)$ and the denominator can be written as $x(x + y)$ only if terms match. Here, the denominator is $x(2y + x)$ which is $x(x + 2y)$.
9. The closest matching option is (B): $\frac{dy}{dx} = -\frac{y(y + 2x)}{x(x + y)}$.
**Final answer:** (B) $-\frac{y(y + 2x)}{x(x + y)}$