Problem 1
No. A nontrivial nullspace violates the Invertible Matrix Theorem.
Faculty use
The Invertible Matrix Theorem
Reward correct mathematics, explicit dimensions/hypotheses, interpretation, and verification. Equivalent valid reasoning should receive credit.
Problem 2
They are independent, A has n pivots, and A is invertible.
Problem 3
Definitions should identify the vector/matrix/space/transformation, dimensions or domain/codomain, and the hypotheses behind linking pivots, nullspace, rank, determinant, eigenvalue zero, and bijectivity. Use the formulas A invertible ⇔ RREF(A)=I; A invertible ⇔ N(A)={0}.
Problem 4
A strong error analysis identifies the first step that violates a definition, dimension, theorem hypothesis, or matrix-operation rule; then repairs that step and re-verifies the final result.
Problem 5
Application responses vary. Require defined variables, a compatible matrix/vector model connected to circuit systems, economic input-output models, repeated solves, and computational reliability, a complete computation, interpretation, and limitations.
Problem 6
Accept two independent checks appropriate to the task: reconstruction, residual, RREF comparison, determinant/rank test, orthogonality, substitution, eigenpair check Av=λv, factorization product, or a second method.
Scoring guidance
Six problems × 10 points: 5 mathematical accuracy, 2 structure/justification, 2 verification/interpretation, 1 notation and communication.