Finding a ring homomorphism...
Find a ring $R$ and an explicit, onto ring homomorphism $f: \Bbb Z[x]
\rightarrow R$ s.t. there is an element $a \in R$ s.t. $5a=1$.
I was thinking use $R=\Bbb Z/4 \Bbb Z$ and sending the polynomial's
constant term $a_0$ to $a_0$ $mod4$. This is definitely onto, but is it a
ring homomorphism? I believe so. And $5$ is $1$ here so there is no issue
there...
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