The circles $O_1$ and $O_2$ do not intersect and do not have the same radius.
$\overline{AB}$ and $\overline{CD}$ are tangent lines of circles $O_1$ and $O_2$, with $A$ and $C$ on the circumference of $O_1$, $B$ and $D$ on the circumference of $O_2$.
Let $\overline{EF}$ be the third tangent line of both circles, with $E$ on the circumference of $O_1$, and $F$ on the circumference of $O_2$,
Extend $\overline{EF}$ to intersect $\overline{AB}$ at $G$ and $\overline{CD}$ at $H$.
Prove that $\overline{GE}$ = $\overline{FH}$
I drew it like this:
I got $AB = CD$ but couldn't find any relations.
Sorry for my bad grammar.

$$GE=AE=AB-BE=CD-EF=CH+HD-(EG+GF)=$$ $$=HG+HF-EG-GF=(HG-GF)+HF-EG=2HF-EG$$ and we are done!