Galois criterion for solving by radicals
Research context
postgraduate concept · established · As of 2026-10-10
Over a field of characteristic zero, a polynomial is solvable by radicals exactly when its splitting-field Galois group is solvable.
Key knowledge
Over a field of characteristic zero, a polynomial is solvable by radicals exactly when its splitting-field Galois group is solvable. A solvable group has a finite normal series with abelian factors. This criterion permits particular quintics with solvable groups and excludes a universal radical formula for the general degree-five polynomial, whose group is S5.
Conditions and scope
- The statement uses characteristic zero and the splitting field, which is normal and separable.
- Failure of a radical expression does not prevent numerical approximation or representations using other functions.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Author checked this English statement, displayed equation where present and stated hypotheses against these source locations: Examples 2.6/2.10 p.29: cubic splitting fields and roots; Example 3.8 p.37: x-cubed minus2 nonnormal real field; Example 4.7 p.49: cubic A3/S3 criterion, applied in the recorded worked example; cyclotomic extensions pp.64–66; solvability Theorem 5.34 pp.76–80. The check is bounded to the recorded claims; no complete proof reconstruction, software proof replay or universal literature completeness is claimed.
2026-10-10 · Author source-body/statement/equation/domain check, with graph associations scoped individually. Separate independent content/source/inventory review is required before branch closure.
Entry details
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