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Apr
8
awarded  Good Question
Apr
5
asked If $N=aP+R$ and $P=bQ+S$, show that $\cfrac{N}{ab}=aS+R$?
Apr
5
answered Why $h\phi (x)$ is analog to $\frac{\partial f}{\partial x}h+ \frac{\partial f}{\partial y}k $?
Apr
3
asked Why $h\phi (x)$ is analog to $\frac{\partial f}{\partial x}h+ \frac{\partial f}{\partial y}k $?
Mar
26
awarded  Popular Question
Mar
21
awarded  Good Question
Mar
19
comment Find two matrices $A,B$ such that $AB=0, BA\neq 0$. What can you say about $(BA)(BA)$?
I made a typo, corrected it now (while laughing for a bit.)
Mar
19
revised Find two matrices $A,B$ such that $AB=0, BA\neq 0$. What can you say about $(BA)(BA)$?
edited body; edited title
Mar
19
asked Find two matrices $A,B$ such that $AB=0, BA\neq 0$. What can you say about $(BA)(BA)$?
Mar
16
comment If $A,B$ are invertible, show that $AB$ is invertible and express $(AB)^{-1}$ in terms of $A^{-1},B^{-1} $.
@Roland Yes. You ask "How to calculate the determinant and make orange juice with it?" and "How to calculate the determinant?" and people think it is a duplicate.
Mar
16
comment If $A,B$ are invertible, show that $AB$ is invertible and express $(AB)^{-1}$ in terms of $A^{-1},B^{-1} $.
@JMoravitz I've read a book on fallacies: "Fallacies and argument apraisal". In it, the author argues that we ended up teaching people that fallacies are bad and must be avoided but it's actually not that simple because in a deeper study, one can observe that there are situations in which fallacies work, that is, are not actually fallacies. I believe the same could be asked on circular logic: Is it always bad? In this case, it helped me yield the correct answer. Is it really a devil that must be avoided at all costs and there are no occasions in which it could be helpful?
Mar
16
revised If $A,B$ are invertible, show that $AB$ is invertible and express $(AB)^{-1}$ in terms of $A^{-1},B^{-1} $.
added 376 characters in body
Mar
13
comment Is it possible to prove uniqueness without using proof by contradiction?
But then, we usually have to prove the uniqueness. Isn't "suppose there are two" (without the different) a contradiction towards the uniqueness?
Mar
13
comment Is it possible to prove uniqueness without using proof by contradiction?
I don't get it. Aren't you imposing the uniqueness instead of proving it? You say that if there are $x,y $ such that $\phi (x)$ and $\phi (y) $, then they are the same. This seems more that you're forcing it to be that way instead of showing it as a consequence of some earlier assumption.
Mar
13
comment Is it possible to prove uniqueness without using proof by contradiction?
@DavidZ I know those aren't proofs. C'mon, I'm stupid but not all that stupid you're expecting.
Mar
13
asked What is the meaning of “perceiving all sets”?
Mar
13
comment Is it possible to prove uniqueness without using proof by contradiction?
@CliveNewstead The empty set, the real numbers zero and one. (Does that answer apropriately?)
Mar
13
comment Is it possible to prove uniqueness without using proof by contradiction?
@CarlMummert Weird. It's often presented as: "Suppose there are two..." - and it really seems a contradiction.
Mar
13
revised Is it possible to prove uniqueness without using proof by contradiction?
edited tags
Mar
13
asked Is it possible to prove uniqueness without using proof by contradiction?