In: Advanced Math
Definition Call a number eld super-constructible if there is a tower of eld extensions,
=0 1 =, where[+1 ]=1,2,or3.
1) Give an example of a eld that is not super-constructible. Prove that your example is correct.
2) Give an example of a super-constructible eld that is not a constructible number eld. Prove that your answer is correct.
a) Let
be the splitting field of
. We know that
and
Thus,
and its only subgroups are
By fundamental theorem of Galois theory, the intermediate fields are as follows:
where
and
. Hence. in particular, there can be no tower
having degree of each extensions..
Thus,
is not super-constructible.
b) Let
be the splitting field of
. We know that
and
Thus,
and its only subgroups are
By fundamental theorem of Galois theory, the intermediate fields are as follows:
where
and
. Hence. in particular, the tower
is such that degree of each extension satisfies.
Thus,
is super-constructible. However, note that it is not constructible
because
is not an integral power of
.