A system of linear equations $AX = B$ (with $A$ square) has a unique solution if and only if:
A$B = 0$
B$|A| = 0$
C$|A| \neq 0$
D$A$ is singular
Answer & Solution
Correct answer: C. $|A| \neq 0$
A unique solution exists iff A is invertible, i.e. |A| ≠ 0 (Cramer/inverse method).
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