三角形内角和定理及其推论在解题中有着广泛的应用.下面举例说明.图1CDREFQP例1如图1所示,平A B面上六个点A、B、C、D、E、F构成了一个封闭的折线图形.求:∠A+∠B+∠C+∠D+∠E+∠F.分析:所求的六个角分布在三个三角形中,但需减去顶点位于P、Q、R处的三个内角,由图形结构不难看 Triangle internal angles and theorems and their inferences are widely used in problem solving. The following examples illustrate. Figure 1 CDREFQP Example 1 As shown in Figure 1, the six points A, B, C, D, E, and F on the plane AB make up A closed polyline pattern. Find: ∠ A + ∠ B + ∠ C + ∠ D + ∠ E + ∠ F. Analysis: The six angles to be found are distributed among the three triangles, but the three points whose vertices are located at P, Q, and R need to be subtracted. Internal angle, not difficult to see by the graphic structure