三角形1. 三角形 ...............................................................................................................21 。 定义 ............................................................................................................ 2 1. 外角和 ........................................................................................................ 2 2. 概念 ........................................................................................................... 2 3. 内角和 ........................................................................................................ 2 2. 分类 ............................................................................................................... 2 1 。 按边 ......................................................................................................... 2 1 。 不等边三菜形 ....................................................................................... 2 2. ................................................................................................................ 2 3 。 ............................................................................................................. 2 2. 按角 ........................................................................................................... 2 1. 锐角三角形 ............................................................................................. 2 2. 钝角三角形 ............................................................................................. 2 3. 直角三角形 ............................................................................................. 2 4 。 ............................................................................................................. 2 3. 性质 ............................................................................................................... 2 1. .............................................................
