学习了“多边形及其内角和”后经常会遇到求很多角的和的问题,比较难做.下面这个“基本图形”因为像一个圆规就叫“规形”吧!(图1,实际上是凹四边形)它有一个重要性质:∠BDC=∠A+∠B+∠C.掌握了这条性质,简直可以“秒杀”这类题目. After learning “polygons and their corners and ” often encounter many angle and the problem is more difficult to do. The following “basic graphics ” because like a compass called “regulation ”! (Figure 1, actually a concave quadrilateral) has one important property: ∠ BDC = ∠A + ∠B + ∠C. Having mastered this property, you can literally ’spike’.