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Equation of a plane

Problem 9.132 · hard

Find an equation of the plane through the points \( \displaystyle (1, -1, 2),\ (-1, -2, -2),\ (2, -3, 2) \).

\[ \left[\begin{matrix}-2\\-1\\-4\end{matrix}\right] \]
PQ.✓ Proved
\[ \left[\begin{matrix}1\\-2\\0\end{matrix}\right] \]
PR.✓ Proved
\[ \left[\begin{matrix}-8\\-4\\5\end{matrix}\right] \]
A normal vector n = PQ × PR (scaled).✓ Proved
\[ 6 \]
n · P gives the constant.✓ Proved
The plane is -8*x - 4*y + 5*z = 6.
Reviewed

Answer \( - 8 x - 4 y + 5 z = 6 \)

✓ Nihil obstat Lines: 4 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	✓ Proved	sympy 1.14.0	simplify(lhs - rhs) reduced to 0
3	✓ Proved	sympy 1.14.0	simplify(lhs - rhs) reduced to 0
4	✓ Proved	sympy 1.14.0	simplify(lhs - rhs) reduced to 0
5	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	all three points satisfy the equation

Reviewers

gpt-oss:20b: pass
qwen3.6:27b-mlx: pass — The solution correctly identifies two vectors lying on the plane, computes their cross product to find a normal vector, and determines the constant term using the dot product with one of the points. The final equation is correct.

Every verdict on record (4)

qwen3.6:27b-mlx: pass 2026-09-27 — The solution correctly identifies two vectors lying on the plane, computes their cross product to find a normal vector, and determines the constant term using the dot product with one of the points. The final equation is correct.
gpt-oss:20b: pass 2026-09-27
qwen3.6:27b-mlx: pass 2026-09-27 — The solution correctly computes the vectors PQ and PR, their cross product to find the normal vector, and the constant term using the dot product. The final equation is correct.
gpt-oss:20b: pass 2026-09-27

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/plane_through_points, checked 2026-09-27 with SymPy 1.14.0.