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In mathematics, a quadratically closed field is a field in which every element of the field has a square root in the field.〔Lam (2005) p. 33〕〔Rajwade (1993) p. 230〕 ==Examples== * The field of complex numbers is quadratically closed; more generally, any algebraically closed field is quadratically closed. * The field of real numbers is not quadratically closed as it does not contain a square root of −1. * The union of the finite fields for ''n'' ≥ 0 is quadratically closed but not algebraically closed.〔 * The field of constructible numbers is quadratically closed but not algebraically closed.〔Lam (2005) p. 220〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「quadratically closed field」の詳細全文を読む スポンサード リンク
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