In: Advanced Math
Show that the map Q[X] → Q[X],
sum^{n}{i=0}(a_nX^i) → sum^{n}{i=0}(a_n(2X + 3)^i) , is an automorphism of Q[X],
Given function ,
We need to show that is an automorphism. We first prove that it is a homomorphism.
Suppose are given by
Then
and
Therefore, is a ring homomorphism.
Thus, to prove that is automorphism, it remains to show that it is bijective. We can do this by showing that has a two-sided inverse.
Consider the function ,
For any element , given by
we have
and
Thus, is a two-sided inverse of . Hence, is an automorphism.