Home›Calculus 3›Implicit differentiation with partial derivatives›Problem 10.518

Implicit differentiation with partial derivatives

Problem 10.518 · easy

Use partial derivatives to find \( \displaystyle \frac{dy}{dx} \) at \( \displaystyle (1, 2) \) for the curve \( \displaystyle x^{2} + x y^{2} = 5 \).

\[ \left[\begin{matrix}\frac{\partial}{\partial x} \left(x^{2} + x y^{2}\right)\\\frac{\partial}{\partial y} \left(x^{2} + x y^{2}\right)\end{matrix}\right] = \left[\begin{matrix}2 x + y^{2}\\2 x y\end{matrix}\right] \]
F_x and F_y.✓ Proved
\[ - \frac{3}{2} \]
dy/dx = −F_x/F_y at the point.✓ Proved

Answer \( - \frac{3}{2} \)

Every line of this solution was proved by the computer algebra system SymPy. The answer was also checked a second way, without looking at the solution. The reviewers disagree about how one step is explained; every verdict is in the receipt.

The full receipt

Line	Status	Checked by	Detail
1	✓ Proved	sympy 1.14.0	simplify(lhs - rhs) reduced to 0
2	✓ Proved	sympy 1.14.0	simplify(lhs - rhs) reduced to 0
answer, a second way	✓ Checked independently	sympy 1.14.0 + mpmath 1.3.0	solved the equation numerically near the point and differenced

Reviewers

gpt-oss:20b: pass
qwen3.6:27b-mlx: fail (error) — The solution fails to explicitly evaluate the partial derivatives at the point (1, 2) to justify the numerical result. While the formula dy/dx = -F_x/F_y is correct, the transition from the symbolic derivatives to the final answer skips the crucial step of substitution, making the logic incomplete and potentially confusing for a student.

Every verdict on record (4)

gpt-oss:20b: pass 2026-10-12
qwen3.6:27b-mlx: fail (error) 2026-10-12 — The solution fails to explicitly evaluate the partial derivatives at the point (1, 2) to justify the numerical result. While the formula dy/dx = -F_x/F_y is correct, the transition from the symbolic derivatives to the final answer skips the crucial step of substitution, making the logic incomplete and potentially confusing for a student.
gpt-oss:20b: pass 2026-10-12
qwen3.6:27b-mlx: pass 2026-10-12 — The solution correctly applies the Implicit Function Theorem formula dy/dx = -F_x/F_y. The partial derivatives are calculated correctly, and the evaluation at (1, 2) yields the correct result.

Proved: SymPy reduced the difference between the two sides to zero. Checked independently: a separate method, named above, confirmed it. Checked numerically: the two sides agree at every sampled point, which is evidence, not proof. Reviewed: a model or a person read it; that is all a sentence can have. Solution by generator:structured/implicit_partials, checked 2026-10-12 with SymPy 1.14.0.