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(詳細はmathematics, a degenerate conic is a conic (a second-degree plane curve, the points of which satisfy an equation that is quadratic in one or the other or both variables) that fails to be an irreducible curve. This can happen in two ways: either it is a reducible variety, meaning that its defining quadratic form is factorable as the product of two linear polynomials, or the polynomial is irreducible but defines not a curve but instead a lower-dimension variety (a point or the empty set); the latter can only occur over a field that is not algebraically closed, such as the real numbers. In the real plane, a degenerate conic can be two lines that may or may not be parallel, a single line (actually two coinciding lines), a single point, or the null set (no points). == Examples == The conic section with equation is an example of the first failure, reducibility. This conic section is degenerate because it is reducible. The equation can be written as , and corresponds to two intersecting lines or an "X". The conic section with equation is an example of the second failure, not enough points (over the field of definition), over the real numbers. This conic section is degenerate because it defines only one point, , not a curve. The conic section with equation is likewise degenerate because it defines the empty set. Over the field of complex numbers, the conic section with equation factors as and is degenerate because it is reducible. 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「degenerate conic」の詳細全文を読む スポンサード リンク
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