# Thread: matrix problem

1. ## matrix problem

Let A be an nxn matrix and n is odd. Show that it is not possible for A2 + I = O.
And what about n is even?

2. ## Re: matrix problem

show your work so far

additionally you might want to restrict $A_{i,j} \in \mathbb{R}$

otherwise

$A=i I_{n,n}$

$A^2 + I = 0$

3. ## Re: matrix problem

For $n$ even a single example will suffice to show it is possibbe for an $n\times n$ matrix $A$ to satisfy $A^2+1=0$. Trial and error or playing with the possibilities will allow you to find a $2 \times 2$ matrix with the required property.