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R0006-03704 · q-20261007-advance-20261009-r07-eigenvalue-0004
Over R, M=[[-9, 1], [-1, 4]] is 2×2. Give its characteristic polynomial coefficients in descending order (λ²,λ,constant).
G001 — Over R, M=[[-9, 1], [-1, 4]] is 2×2. Give its characteristic polynomial coefficients in descending order (λ²,λ,constant).Use the original question domain, assumptions and cited MKO definitions. This item has second-context mathematical and bilingual review, with the model, answer and every arithmetic step independently recomputed from the original parameters; the source question remains a candidate.
Before
[[-9, 1], [-1, 4]]
After
exact real2×2 matrix;no spectrum or diagonalization inferred
Conditions: none
Use the declared real2×2 matrix;coefficients,a discriminant or one candidate residual does not automatically establish the entire spectrum or diagonalizability.
Rule: two_by_two_matrix_scope · Uses: G001
Before
trace := sum(-9, 4)
After
trace = -5
Conditions: none
The trace is the sum of diagonal entries.
Rule: exact_rational_arithmetic · Uses: G001, S001
Before
diagonal product := mul(-9, 4)
After
diagonal product = -36
Conditions: none
Compute the determinant term a·d.
Rule: exact_rational_arithmetic · Uses: G001, S002
Before
off-diagonal product := mul(1, -1)
After
off-diagonal product = -1
Conditions: none
Compute b·c,which must be subtracted rather than added.
Rule: exact_rational_arithmetic · Uses: G001, S003
Before
determinant := sub(-36, -1)
After
determinant = -35
Conditions: none
Compute ad−bc exactly.
Rule: exact_rational_arithmetic · Uses: G001, S004
Before
negative trace := mul(-1, -5)
After
negative trace = 5
Conditions: none
The linear coefficient of det(tI−M) is−trace,including its sign.
Rule: exact_rational_arithmetic · Uses: G001, S005
Before
det(tI−M)=(t−-9)(t−4)−(1)(-1)
After
t²+(5)t+(-35)
Conditions: none
Expand the2×2 determinant to get descending coefficients(1,−trace,det).Keep this order and the negative trace;the coefficients alone do not establish diagonalizability.
Rule: characteristic_polynomial_expansion · Uses: G001, S006
S007 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.S006 · premise_and_result_audit — Recompute negative trace with exact rational arithmetic, not rounded decimals.S005 · premise_and_result_audit — Recompute determinant with exact rational arithmetic, not rounded decimals.S004 · premise_and_result_audit — Recompute off-diagonal product with exact rational arithmetic, not rounded decimals.S003 · premise_and_result_audit — Recompute diagonal product with exact rational arithmetic, not rounded decimals.S002 · premise_and_result_audit — Recompute trace with exact rational arithmetic, not rounded decimals.S001 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.(1, 5, -35)
The full substitutions and premise checks give the original answer; source identity,format and status are unchanged.
Review date: 2026-10-26
Original questions, answers, step expressions, numeric ASTs and historical records are retained. Source candidate labels remain historical and are not overwritten as formal proof.
input commit: 0f7be61e2c22317a4075561dc822c87d881a50dboriginal question SHA-256: c3da3247b23a5ff4bb2eb4f3015c22cfcb065c40e96b39c5cd54d0601f508821candidate record SHA-256: b2b387138ae5b238a7977313d9667824386839d36cd7b1230b3c164fd9266616semantic review receipt SHA-256: 568eefd71709ac3dc16a0d5b3b4ad3e83376a8ef300c9e5493eee0721500b29dquestion-first witness SHA-256: d964b91bedb9d4918bbc055f567762a09f5a58af6c876268e719d5100332d855Lean: NOT_RUN · human review: NOT_PERFORMED