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Second derivatives of parametric curves

Problem 8.131 · medium

For \( \displaystyle x = \frac{t^{2}}{2} \), \( \displaystyle y = \frac{t^{3}}{3} \), find \( \displaystyle \frac{dy}{dx} \) and \( \displaystyle \frac{d^2y}{dx^2} \) at \( \displaystyle t = 3 \).

\[ \frac{\frac{d}{d t} \frac{t^{3}}{3}}{\frac{d}{d t} \frac{t^{2}}{2}} = t \]
dy/dx = (dy/dt)/(dx/dt).✓ Proved
\[ \frac{\frac{d}{d t} t}{\frac{d}{d t} \frac{t^{2}}{2}} = \frac{1}{t} \]
d²y/dx² = [d/dt (dy/dx)] / (dx/dt).✓ Proved
\[ \left[\begin{matrix}3\\1 \cdot \frac{1}{3}\end{matrix}\right] = \left[\begin{matrix}3\\\frac{1}{3}\end{matrix}\right] \]
At t = 3.✓ Proved

Answer \( \frac{dy}{dx} = 3,\ \frac{d^2y}{dx^2} = \frac{1}{3} \)

✓ Nihil obstat 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. Reviewers found nothing wrong with the explanation.

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
3	✓ 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	y found as a function of x by inverting x(t) numerically, then differenced

Reviewers

gpt-oss:20b: pass
qwen3.6:27b-mlx: pass — The solution correctly applies the formulas for first and second derivatives of parametric equations and evaluates them at t=3.

Every verdict on record (4)

gpt-oss:20b: pass 2026-10-06
qwen3.6:27b-mlx: pass 2026-10-06 — The solution correctly applies the formulas for first and second derivatives of parametric equations and evaluates them at t=3.
gpt-oss:20b: pass 2026-10-06
qwen3.6:27b-mlx: pass 2026-10-06 — The solution correctly applies the formulas for first and second derivatives of parametric equations and evaluates them at t=3.

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/parametric_second_derivative, checked 2026-10-06 with SymPy 1.14.0.