Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2021/iii/paper-136/3/b/ii/solution

Let
The extension is the unramified quadratic extension. Since contains all st roots of unity, is a cyclic, tamely and totally ramified extension of degree , with automorphisms .
The Frobenius automorphism of extends by fixing and conjugates to . Hence is Galois, its inertia group is
and its residue-field Galois group is
The tame ramification also gives .

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