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Homework Help: Discrete Math Help

  1. Jan 28, 2007 #1
    1. The problem statement, all variables and given/known data

    f: B => C and g: A => B

    1. If f of g is injective, then f is injective.

    2. If f of g is injective, then g is injective.

    2. Relevant equations

    3. The attempt at a solution

    I know that 1 is true and 2 is false because I found those as properties, but I am not exactly sure why, and I do not know how to show a proof.

    Any help please?
  2. jcsd
  3. Jan 29, 2007 #2
    If f of g is injective then every x,y in A such that f(g(x)) = f(g(y)) implies that x=y.

    I suggest from here to suppose that f or g is not injective and come up with a contradiction. Ie: suppose f is injective and g is not injective, suppose f is not injective and g is injective, suppose f and g are not injective. Work it out from here.
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