allerySystem of equations Ax = b has unique solution iff:
AMore equations than unknowns
Bb = 0
C|A| ≠ 0 (A is non-singular, equivalently invertible)
D|A| = 0
Answer & Solution
Correct answer: C. |A| ≠ 0 (A is non-singular, equivalently invertible)
**For square A:** unique solution iff |A| ≠ 0 (then x = A⁻¹ b).
If |A| = 0: either no solution (inconsistent) or infinitely many (under-determined).
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