# Help with composition proof

• Sep 20th 2009, 01:04 PM
Dax
Help with composition proof
I am in discrete structures and have to solve this proof and have been having a fairly difficult time with it, probably easy but math was never my strong suit.

If f: A--->B is a bijection and g: B--->C is injective, prove that g
o f is injective.

• Sep 20th 2009, 01:09 PM
Plato
Quote:

Originally Posted by Dax
I am in discrete structures and have to solve this proof and have been having a fairly difficult time with it, probably easy but math was never my strong suit.
If f: A--->B is a bijection and g: B--->C is injective, prove that g
o f is injective.

Start with $g \circ f(a) = g \circ f(b)$.
Does that mean $f(a) = f(b)$? WHY?
Finish.