Results 1 to 2 of 2

Math Help - Injection/Surjection

  1. #1
    Member
    Joined
    Oct 2008
    Posts
    93

    Injection/Surjection

    Let f : A -> B and g : B -> C be two functions.
    (a) If g o f is injective, must g be injective ? Give a proof or a counterexample.
    (b) If g o f is injective, must f be injective ? Give a proof or a counterexample.

    a) So here's what I think i'm doing im not sure if it's right

    if g o f is injective then there exists
    x in g o f such that, x1 = x2
    (g(f(x1)) = (g(f(x2))


    but i cant go to g(x1) = g(x2) cus i dont know if f isinjective so I dont know how to continue b I start the same way but i get stuck again
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Mar 2010
    From
    Florida
    Posts
    3,093
    Thanks
    5
    Second question of the pdf file.
    Attached Files Attached Files
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Injection implied by Surjection
    Posted in the Number Theory Forum
    Replies: 4
    Last Post: April 5th 2011, 09:16 PM
  2. Injection and Surjection
    Posted in the Advanced Algebra Forum
    Replies: 15
    Last Post: January 7th 2010, 07:44 AM
  3. injection, surjection and bijection questions
    Posted in the Discrete Math Forum
    Replies: 1
    Last Post: November 7th 2009, 11:23 AM
  4. Prove injection and surjection
    Posted in the Advanced Algebra Forum
    Replies: 2
    Last Post: May 31st 2009, 08:48 PM
  5. injection & surjection proofs
    Posted in the Discrete Math Forum
    Replies: 2
    Last Post: April 15th 2009, 06:01 AM

Search Tags


/mathhelpforum @mathhelpforum