Matrices: Dependency of AB on A&B

I have no idea how to approach this.
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33 Replies
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Gamertug
Gamertug3w ago
its A i mean is it A cummute means on multipilcation order doesnt change , LHS they are being multiplied and in RHS they are being added , ORder of A = Order of B if they are addable And that means Order of AB = Order of A = Order of B
SirLancelotDuLac
SirLancelotDuLacOP3w ago
Its A,B and C.
Gamertug
Gamertug3w ago
oh
SirLancelotDuLac
SirLancelotDuLacOP3w ago
Wait order doesn't mean its true tho? Since that would be true for all square matrices of the same order which is not the case. (For instance if B=-A, A^2 need not be k.A for some real k)
Gamertug
Gamertug3w ago
it is true for all square matrices all square matrices are cummute only same order matrices can be added and AB = some matrix , then there order must also be same i got A - bI = a|AB^-1| if u prove AB^-1 = not equal to 0 then its solved |A/B| = not equal to 0
SirLancelotDuLac
SirLancelotDuLacOP3w ago
How do we prove that |A/B|≠0?
Gamertug
Gamertug3w ago
i cant think of anything at the moment i will go eat and brb
SirLancelotDuLac
SirLancelotDuLacOP3w ago
How so?
Gamertug
Gamertug3w ago
ok look Matrix A = nxn (Order) B = nxn AB = nxn(Order) Hence after mutliplying its the same as it was before i think there might be some missing condition , there isnt any info on A , B Except that they are sq matrix
SirLancelotDuLac
SirLancelotDuLacOP3w ago
Order doesn't tell anything tho no?
SirLancelotDuLac
SirLancelotDuLacOP3w ago
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Gamertug
Gamertug3w ago
cummute is all about order tho
SirLancelotDuLac
SirLancelotDuLacOP3w ago
Here AB≠BA
Gamertug
Gamertug3w ago
we talking about order only not values AB = BA = A = B Order only for commute @SirLancelotDuLac
Gamertug
Gamertug3w ago
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SirLancelotDuLac
SirLancelotDuLacOP3w ago
AB must be equal to BA which is not always the case
Gamertug
Gamertug3w ago
nooo
SirLancelotDuLac
SirLancelotDuLacOP3w ago
For instance, this case
Gamertug
Gamertug3w ago
Order (AB) = Order (BA) We talking abt order only wait nvm i get it now mb i read it wrong
SirLancelotDuLac
SirLancelotDuLacOP3w ago
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Gamertug
Gamertug3w ago
these silly mistakes are getting out of hand man wth it seems like there is no info i will ask my teachers
Opt
Opt3w ago
@SirLancelotDuLac did you get this?
SirLancelotDuLac
SirLancelotDuLacOP3w ago
Nope.
Opt
Opt3w ago
The major problem I'm finding here is that we cannot assume A and B are nonsingular If we can do that, options b and c become trivial
Gamertug
Gamertug3w ago
yes
Opt
Opt3w ago
@SirLancelotDuLac @Gamertug asked my teacher and he got b,c. He said he'll try a as well.
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Opt
Opt3w ago
It's embarrassingly simple lol
SirLancelotDuLac
SirLancelotDuLacOP3w ago
Ah thanks a lot, mate. Fr Oh I got A is well From this (B-aI)(A-bI)=abI so AB=BA on simplifying.
Opt
Opt3w ago
Because of the order in which you factorise? Yeah, that works out ig
SirLancelotDuLac
SirLancelotDuLacOP3w ago
Yeah. +solved @Opt
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