(e+f)^2 = e^2+2ef+f^2
Why is this not neccesary true for squares matrices for all size?
(e+ f)^2= (e+f)(e+f)= e^2+ fe+ef+ fe. Remember that multiplication of matrices is not, in general, commutative!
Do you mean (e+f)2 = e2+fe+ef+f2? I might be misinterpreting it but I can't see where that extra "fe" came from and where the "f2" went.
Yeah, that's what he meant: (e+f)² = e² + ef + fe + f².
One of these days, I'm going to learn to type!
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