Question 9 • Advanced Algebra: Concepts and Connections
For a 2 by 2 matrix [0m[[a,b],[c,d]], the inverse is 1/(ad−bc) times [[d,−b],[−c,a]]. The first matrix has determinant 6(−4)−14(−2)=4, so its inverse is [[−1,−7/2],[1/2,3/2]]. Matching the lower-left entry with the second matrix gives y=1/2, choice A.
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