Composite Functions: Is (f o g)^-1 = gof?

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    Composite Functions
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Discussion Overview

The discussion centers on the properties of composite functions, specifically whether the inverse of the composition of two functions, (f o g)^-1, is equal to the composition of their inverses, gof. Participants explore the validity of this statement and seek counterexamples or clarifications.

Discussion Character

  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions the truth of the statement (f o g)^-1 = gof and requests a counterexample if it is false.
  • Another participant asserts that while the first part of the statement is true, the second part is false, suggesting that the entire statement is false due to its "and" nature.
  • A different participant claims that fog is not a function and emphasizes that composition reads from right to left, asserting that gof is indeed a function.
  • Another participant clarifies that gof is a function from A to C and states that (gof)^-1 does not equal fog, explaining that the domains do not align for this equality to hold. They propose that (gof)^-1 = f^-1 o g^-1 instead, noting that both expressions map from C to A.

Areas of Agreement / Disagreement

Participants express disagreement regarding the validity of the statement (f o g)^-1 = gof, with multiple competing views on the properties of composite functions and their inverses. No consensus is reached on the correctness of the claims made.

Contextual Notes

Participants discuss the implications of function composition and inverses, highlighting potential misunderstandings regarding the domains and mappings involved. There is uncertainty about how inverses affect the composition of functions.

Monsu
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If f:A -> B and g:B -> C are functions, is this true: f o g is also a function and (f o g) ^-1 = gof

I think this isn't true, but if this isn't the case, could someone please tell me a counter example?? Thanks
 
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the first part is true, but the send part is false. since it is an and statement the entire statement is false. if it were an or statement, it would be true.

I think I am right but I can't remember right now if the mapping from A to B gets changed when you take the inverse or what. either way, it should not be a function any more.
 
fog is not a function, composition reads from right to left. gof is a function.
 
Assuming f:A->B and g:B->C then gof is a function from A to C.

No, it is NOT true that (gof)-1= fog. As matt grime pointed out, that's not even a function: g goes from B to C and C is not the domain of f.

What IS true, in this case, is that (gof)-1= f-1og-1 which is probably what you meant.

Notice that, since f:A->B, f-1:B->A and, since g:B->C, g-1:C->B. That means that both (gof)-1 and f-1og-1 are from C to A.
 

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