人教版九年级数学全册知识点.docx

人教版九年级数学全册知识点 Chapter 21 Quadratic Equations 21.1 Quadratic Equations An equation that contains only one unknown and the highest power of the unknown is 2 is called a quadratic equation. A quadratic equation has four characteristics: (1) it contains only one unknown, (2) the highest power of the unk