Projections and orthogonality
Problem 9.344 · medium
Find \( \displaystyle \operatorname{proj}_{\mathbf v} \mathbf u \) for \( \displaystyle \mathbf u = \left\langle -4, -1, 3 \right\rangle \), \( \displaystyle \mathbf v = \left\langle 5, -4, -1 \right\rangle \).
- \[ -20 - 3 + 4 = -19 \]u·v.✓ Proved
- \[ 1 + 16 + 25 = 42 \]‖v‖².✓ Proved
- \[ \left[\begin{matrix}- \frac{95}{42}\\\frac{38}{21}\\\frac{19}{42}\end{matrix}\right] \]proj = (u·v/‖v‖²) v.✓ Proved
Answer \( \left\langle - \frac{95}{42}, \frac{38}{21}, \frac{19}{42} \right\rangle \)
✓ 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 | the remainder is orthogonal to v and the projection is parallel to it |
Reviewers
gpt-oss:20b: passqwen3.6:27b-mlx: pass — The solution correctly applies the vector projection formula and the arithmetic is verified by the algebra system.
Every verdict on record (4)
gpt-oss:20b: pass 2026-10-07qwen3.6:27b-mlx: pass 2026-10-07 — The solution correctly applies the vector projection formula and the arithmetic is verified by the algebra system.gpt-oss:20b: pass 2026-10-07qwen3.6:27b-mlx: pass 2026-10-07 — The solution correctly applies the vector projection formula and the arithmetic is correct.
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 2026-10-07 with SymPy 1.14.0.