Home›Calculus 3›Projections and orthogonality›Problem 9.423

Projections and orthogonality

Problem 9.423 · easy

Which pairs of \( \displaystyle \mathbf a = \left\langle -3, -6, 4 \right\rangle \), \( \displaystyle \mathbf b = \left\langle -52, 10, -24 \right\rangle \), \( \displaystyle \mathbf c = \left\langle 6, 6, -4 \right\rangle \) are orthogonal?

\[ \left[\begin{matrix}0\\-70\\-156\end{matrix}\right] \]
a·b, a·c, b·c.✓ Proved
Two nonzero vectors are orthogonal exactly when their dot product is 0.
Reviewed

Answer \( \mathbf a \perp \mathbf b \)

✓ Nihil obstat Lines: 1 proved, 1 reviewed. 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	Reviewed	reviewers: gpt-oss:20b, qwen3.6:27b-mlx	a sentence; read, not computed
answer, a second way	✓ Checked independently	sympy 1.14.0 + mpmath 1.3.0	dot products recomputed

Reviewers

gpt-oss:20b: pass
qwen3.6:27b-mlx: pass — The solution correctly computes the dot products and applies the definition of orthogonality. Since only a·b is 0, the conclusion that only a and b are orthogonal is correct.

Every verdict on record (4)

gpt-oss:20b: pass 2026-10-08
qwen3.6:27b-mlx: pass 2026-10-08 — The solution correctly computes the dot products and applies the definition of orthogonality. Since only a·b is 0, the conclusion that only a and b are orthogonal is correct.
gpt-oss:20b: pass 2026-10-08
qwen3.6:27b-mlx: pass 2026-10-08 — The solution correctly identifies the orthogonality condition and implicitly uses the computed dot products to conclude that only a and b are orthogonal (since a·b = 0).

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/vector_projection, checked 2026-10-08 with SymPy 1.14.0.