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Sorry, but I'm in dire need(Proofs) 
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#1
May1606, 12:28 AM

P: 62

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. 


#2
May1606, 12:56 AM

P: 304

Both can be done easily by contradiction.



#3
May1606, 01:02 AM

HW Helper
P: 2,954

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 


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