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Questions about the properties of vector spaces and linear transformations, including linear systems in general.

24 votes

Example for column rank $\neq$ row rank

I will only consider matrices over division rings, since defining rank over more general rings, in particular those with zero divisors, involves difficulties rather independent of those posed by non-c …
Marc van Leeuwen's user avatar
0 votes

Kernel of $AB$ if $[A,B]=0$ and $AB\neq0$?

Here is an intuitive way to see why this must be false. You want to establish an equality, so your (dependent) inequalities 2) and 4) are suspect; inequalities are seldom useful in proofs of equalitie …
Marc van Leeuwen's user avatar
6 votes

Expressing $-\operatorname{adj}(A)$ as a polynomial in $A$?

This formula can be obtained during a proof of the Cayley-Hamilton theorem, as is indicated on its Wikipedia article. The essence of the argument is that Euclidean division by a monic polynomial (on t …
Marc van Leeuwen's user avatar