Answer: (A) CDD
if D=C^-1
then
C D D = (C C^-1) D = I D = D
(where I is the identity matrix)
Solving for "y" means that we need to get y to be on one side of the equation. It should look like y= something. To get the y by itself, we need to get rid of that -3. To do that, we'll have to divide by -3 (because even though there's a y being divided, the -3 is still the numerator). 6/-3 is -1/2. Therefore your answer is y=-1/2
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