Thread: matrices

for which value of x is this matrix invertible:

1 0 2
2 x 2
2 1 (x+1)

Determinant of this matrix = 0

I've worked out that x must be +1 or +2 but I'm stuck on where to go from there

You're doing OK. In order to be invertible, the determinant can't be 0.

It is 0 at x=1 and x=2. Therefore, all other values must be in the domain of invertibility.