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

  1. May 16, 2006 #1
    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. jcsd
  3. May 16, 2006 #2
    Both can be done easily by contradiction.
  4. May 16, 2006 #3


    User Avatar
    Homework Helper

    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 :
    Last edited: May 16, 2006
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Similar Discussions: Sorry, but I'm in dire need(Proofs)
  1. Need proof (Replies: 1)