确定一个二次曲线：Ａｘ２＋Ｂｘｙ＋Ｃｙ２＋Ｄｘ＋Ｅｙ＋Ｆ＝０一般需五个独立条件，因此，经过四点的二次曲线一般情况下有无数条，它们组成一个二次曲线系；本文以定理形式介绍一种新的二次曲线系，并举例说明其应用，并以此引伸出一种新的解题方法；１．定理的证明定理　 A quadratic curve is determined: Ax2+Bxy+Cy2+Dx+Ey+F=0 generally requires five independent conditions. Therefore, after four points of the quadratic curve, there are innumerable strips. They form a quadratic curve system; this paper introduces a new two in the form of a theorem. Sub-curve system, and examples of its application, and to introduce a new solution method; Proof Theorem