Composite Function Homework: Proving One-to-One & Onto

[nikie1o2]

Homework Statement

let A,B,C be sets, and let f : A--> B and g : B--> C be functions. The composite function denoted by g o f is a function from A to C defined as follows:

Homework Equations

g o f(x)=g(f(x)) for every x in A.

Prove that if g o f is one-to one, then f is one-to one
Prove that is g o f is onto, then g is onto

The Attempt at a Solution

I really don't know how to approach this problem. I didnt things similar with binary structures determining if they are an isomorphism by not familiar with composite functions

 

[polarbears]

I think I know how to approach it...check me if I'm right though

check if its one-to-one and onto

if it is one-to-one that implies if f(a)=f(b) then a=b