# Discrete Math Help

1. Jan 28, 2007

### swears

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.

2. Jan 29, 2007

### moo5003

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.