I've been trying to prove that the set of all invertible $n \times n$ matrices is a differentiable manifold. My attempt is as follows:
Define a map $\alpha : X \to XX^{-1} - I$
I take the inverse: $\alpha^{-1}(0)$ which would map to the set of invertible $n \times n$ matrices. I believe this suffices to show it is a manifold, but I am stumped in finding it's dimension. How can I approach this?