- #1
geoffrey159
- 535
- 72
Homework Statement
Show that any hyperplane of ##M_n(\mathbb{C})## contains at least an invertible matrix
Homework Equations
Let ##H## be an hyperplane of ##M_n(\mathbb{C})##.
The Attempt at a Solution
By contradiction, assume that for any matrix ##A\in H##, ##A## is not invertible.
Therefore 0 is an eigenvalue of A, and there exists a basis of ##M_{n,1}(\mathbb{C})## in which at least the first column of ##A## is 0.
This can be translated to : there is a surjection ##\phi## between the vector space ##U = \{ M\in M_n(\mathbb{C}) : \forall i = 1...n\ m_{i1} = 0 \} ## and hyperplane ##H##.
My problem to obtain a contradiction is that ##\phi## is not linear. If it was I would use the rank theorem and
## n^2 - 1 = \text{dim}(H) = \text{rk}(\phi) \le \text{dim}(U) = n^2 -n ##
which is a contradiction as soon as ##n\ge 2##.
How would you solve this ?