Sorry, but I'm in dire need(Proofs)

  • Thread starter QuantumDefect
  • Start date
In summary, the conversation discusses the need for help with proving two statements involving the injectivity and subjectivity of functions. The conversation suggests using a proof by contradiction and referencing Wikipedia pages for definitions and mappings.
  • #1
QuantumDefect
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Hello, I need some help. Could someone kick me(hard please) in the right direction here? Here are the statements I need to prove:
1) If g of f is injective, then f is injective
2) If g of f is subjective, then g is subjective

where g and f are functions where f:A->B and g:B -> C where A,B and C are sets

Any kicks in the right direction would be GREATLY appreciated. Thank you.
 
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  • #2
Both can be done easily by contradiction.
 
  • #3
Start with the definitions of injections and surjections (note the spelling of the latter), and draw functional mappings (domain/codomain diagrams). The proof is fairly easy from inspecting the mappings.

Wikipedia has fairly good pages on these subjects, complete with the mappings you need for the proof : http://en.wikipedia.org/wiki/Injective_function

http://en.wikipedia.org/wiki/Surjection
 
Last edited:

What do you mean by "Sorry, but I'm in dire need(Proofs)"?

This phrase is typically used when someone urgently needs evidence or proof to support their claims or arguments.

Why would someone use this phrase?

This phrase may be used when a person is facing skepticism or doubt about their statements and needs to provide evidence to back them up.

What kind of proofs are usually requested?

The type of proofs requested may vary, but they often include data, statistics, experiments, or other forms of evidence that support the person's claims.

Who typically asks for proofs?

Anyone who is skeptical or doubtful about a person's claims may ask for proofs. This could include colleagues, peers, or even the general public.

How should one respond to this phrase?

The best way to respond is to provide the requested proofs in a clear and concise manner. It is important to remain calm and professional, and to avoid becoming defensive or confrontational.

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