What is this in regards to? What field are we working in? Matricies?
The definition of , in general, (matrices, elements of a group or field, etc.) is that if and only if and where I is the "multiplicative identity" for the algebraic structure. T
If you know that then you know that and [mathy]BA= I[/tex], by replacing X above with A and Y with B. But if we were to replace X with B and Y with A, we wold get exactly the same equations!