三角形,定义为:三线段,首尾连,封闭图.有特性:不变性,不变形,稳定性.三顶点,三个角,三条边,九元素;用符号,来表示,一顶点,大字母;一个角,三大写,一小写,一西腊,一数字,皆可以;一小写,两大写,表示边.内角和,一百八,外角和,三百六.两边和,大第三,两边差,小第三,角与边,有关系,较大角,对大边.三边和,是周长,底与高,积一半,为面积.两边等,是等腰,所对角,也相等:对称轴,有一条;顶角有,平分线,底中线,底边高,三合一.三边等,为等边,正 Triangle, defined as: the three-line segment, the first and last even, closed map. Have the characteristics: invariance, deformation, stability. Three vertices, three corners, three edges, nine elements; with symbols to indicate that a vertex, ; A corner, the three uppercase, lowercase, a West, a number, can be; a lowercase, two uppercase, said the edge of the inner corner and, one hundred eighty, outer corner and three hundred and six. On both sides of the poor, small third, the corner and the side, the relationship between the larger angle on the big edge. Trilateral and, is the perimeter, at the end with the high, plot half, for the area. Both sides are isosceles, diagonal, Also equal: the axis of symmetry, there is a; vertex angle, bisector, the bottom line, the bottom of the high, triple. Trilateral, etc., for the equilateral, positive