Prove: Ï† is an isomorphism

**I already showed it is bijective. Now, I need help proving the homomorphism part. I know by definition for all a,b in G, f(ab)=f(a)f(b)**

__What I Know:__**How do I show this? For some reason I am getting confused and I don't think it's that difficult but I can't grasp it.**

__Question:__**Let a=gag^-1 and b=gbg^-1. Then f(ab)=f(gag^-1 * gbg^-1) Is this even correct or did I start off totally wrong?**

__What I Have Done:__Thanks!!