I am looking at the following: $$$$ $$$$ I haven't really understood the proof... Why do we consider the differential equation $y'=P(x)y$ ? Why does the sentence: "If ...
Let $R$ be a ring. Then I would like to know the units in $M_n(R)$. Here is my idea. The determinant is a homomorphism from $M_n(R)$ to $R$. If $A$ is a unit, then there is a $B$ such that $AB = I$. ...