Let $A,B$ be groups with a homomorphism $h: A \to B$. Let $x,y \in A$.
I'm supposed to show that if $h(x)$ has finite order in $B$, then ${\rm order}(x)$ is infinite or ${\rm order}(h(x))$ divides ${\rm order}(x)=n < \infty$.
And of course the answer is
https://proofwiki.org/wiki/Element_to_Power_of_Multiple_of_Order_is_Identity
https://proofwiki.org/wiki/Order_of_Homomorphic_Image_of_Group_Element
What I'm wondering is the relevance of the assumption '$h(x)$ has finite order in $B$'. I think the only role it serves to make '${\rm order}(h(x))$' well-defined because actually I think the statement
${\rm order}(x)$ is infinite or ${\rm order}(h(x))$ divides ${\rm order}(x)$
is ('sensible' and) true because ${\rm order}(x) < \infty \implies{\rm order}(h(x)) < \infty$.
Questions:
Is the statement "${\rm order}(x)$ is infinite or ${\rm order}(h(x))$ divides ${\rm order}(x)$" true?
If not, then why not? If so, then am I right about the role of the assumption that ${\rm order}(h(x)) < \infty$ ?
Can we just say instead like
Show that if ${\rm order}(x) < \infty$, then
(A) ${\rm order}(h(x)) < \infty$ because ${\rm order}(h(x)) \le{\rm order}(x)$
- (the $(h(x))^n = h(x^n=1_A)=1_B$ part)
(B) ${\rm order}(h(x))$ divides ${\rm order}(x)$
- (the division algorithm part)
?