平行线的性质定理:如果两直线平行,那么同位角相等;内错角相等;同旁内角互补。平行线的判定定理:如果同位角相等,内错角相等,同旁内角互补,　那么两直线平行。一、两定理共用一个图形平行线的性质与判定都是建立在两条直线被第三条直线所截时形成的“三线八角”图的基础上,要学 The property theorem of parallel lines: If two straight lines are parallel, then the isotropic angle is equal; the inner angle is equal; and the inner and outer angles are complementary. The decision theorem of parallel lines: if the azimuth angles are equal, the internal angles are equal, and the internal angles are complementary, the two lines are parallel. The property and judgment of sharing a graph parallel line between one and two theorems are based on the “three-line octagonal” diagram formed when two straight lines are cut by the third straight line.