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Vectors in three dimensions

Problem 9.365 · easy

For \( \displaystyle \mathbf a = \left\langle 2, -5, 5 \right\rangle \) and \( \displaystyle \mathbf b = \left\langle 1, 0, -1 \right\rangle \), find \( \displaystyle 3\mathbf a - (4)\mathbf b \) and \( \displaystyle \|\mathbf a - \mathbf b\| \).

\[ \left[\begin{matrix}2\\-15\\19\end{matrix}\right] \]
Componentwise.✓ Proved
\[ \sqrt{62} \]
‖a − b‖.✓ Proved

Answer \( \left\langle 2, -15, 19 \right\rangle,\ \sqrt{62} \)

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	floating point

Reviewers

gpt-oss:20b: pass
qwen3.6:27b-mlx: fail (error) — The solution provides no derivation or explanation for how the results were obtained, merely stating the final answers as identities. It fails to show the vector arithmetic or norm calculation required by the problem.

Every verdict on record (4)

gpt-oss:20b: pass 2026-10-07
qwen3.6:27b-mlx: fail (error) 2026-10-07 — The solution provides no derivation or explanation for how the results were obtained, merely stating the final answers as identities. It fails to show the vector arithmetic or norm calculation required by the problem.
qwen3.6:27b-mlx: pass 2026-10-07 — The solution correctly computes the vector linear combination and the norm of the difference vector. The results match the stated answer.
gpt-oss:20b: pass 2026-10-07

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/vectors_space, checked 2026-10-07 with SymPy 1.14.0.