I have a 3x3 matrix:

1, -2, 0

k, 1, k

0, -2, 1

and I have to find all values of K that make the matrix non-invertible. I know matrices are non-invertible when 2 rows are proportionate, but (in my mind) this won't work in the matrix given because no 2 rows will be proportionate for a single k value. This answer is however marked incorrect when input in WileyPlus (online math questions thing).

If anyone has insight into if there is actually an answer and I'm missing it or can provide more insight that would be great!

cheers