Figure 3.2.Symmetries of a triangle B B identity id= B A B C 第二例： A B rotation A B B rotation A C B B reflection Table 3.2.Symmetries of an equilateral triangle 0 id P1 p2 μ1 2μ3 A B id id P1 p2 41 2 3 9 P1 B P2 id 3 1 2 B P2 id ps 2 3 1 reflection 1 2 3 id P2 2 2 3 P2 d A 3 山 2 id B A reflection = AB A C B第二例：