# Practice Quiz Question 9 - Calculate the determinant of the inverse of the output matrix AB that you selected in Q8

The question: Calculate the determinant of the inverse of the output matrix AB that you selected in Q8.

the correct answer for question 8 is : [[33,-1,-20],[9,-5,4],[-6,2,0]].

Question 8 was asking for the product of two matrices.

I took this practice quiz twice but never really understood why I got question 9 wrong. I have a hint that determinates just do not have an inverse in the context of a matrix manipulation/singularity or have no utility.

At first I guessed det(AB)^-1 = 1 , because I was thinking any number other than 0 would be correct.
Then I guessed det(AB)^-1 = 0 because maybe I was just dead wrong on my first guess.
But that also isnt the case so what I’m left with is

det(AB) cannot be computed
or
det(AB)^-1 cannot be computed

Thank you for the help.

The determinate was zero and you cant get an inverse of zero. I shouldve considered this possibility first. If I am wrong in calculating the determinant please let me know.