# Question 2: Inverse of matrix

For the section " Determinants and Linear Transformations" I am completely puzzled with the second question:

{moderator edit - quiz question removed}

Since this comes after a section where we learned about correlations related to the determinant, I somehow assume that it’s related to the that.

When we earlier learned about calculating the inverse matrix we did that with a 2x2 matrix. I approached doing this for 3x3 and that seems quite cumbersome.

Either I should just go ahead and do that calculation or I am missing something extremely obvious (that is my fear).

Could somebody point me to the right direction please?

I have not taken that class, so I have not taken that quiz and don’t know what the W matrix looks like. But the high level point is that not all square matrices are invertible. How do you tell if a matrix is invertible? There is a simple way, right? They must have covered that in the lectures.

If the matrix passes the test and you know it should be invertible, then you could also just multiply it by each of the matrices shown and see if you get the identity matrix or not.

Just some thoughts, with the disclaimer as mentioned above!

Thanks for your answer. I do believe based on “rules” you hinted the inverse can be calculated.

My issue was that they say “calculate” in the task and said calculation is quite an undertaking and I got unsure if that’s really what is expected of us - since the total quiz is supposed to take 30m.

“then you could also just multiply it by each of the matrices shown and see if you get the identity matrix or not.”
Oh indeed. I know all the mechanics, but I was silly not to realize I could just plug them and see what I get

Many thanks, now it’s resolved!

That’s what I did when I took the quiz. It was cumbersome.
Later on I started using a calculator that computes the determinant.