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凸四边形内角和定理证明的基本思路是利用化归法,将四边形转化为三角形,然后利用三角形内角和为180°,达到证明的目的,而这种证明思路正是研究四边形,乃至多边形的基本方法.现列举几种不同证法如下. 四边形内角和定理:四边形的内角和为360°. 已知:四边形ABCD, 求证:∠A+∠B+∠C+∠D=360°. 注:为书写简便,记三角形内角和为∑,
The basic idea of the internal angle of the convex quadrilateral and theorem proving is to convert the quadrilateral into a triangle by using transformation and then use the triangle internal angle and 180° to achieve the purpose of the proof. This proof is the basic method for studying the quadrilateral and even the polygon. Here are some examples of different authentication methods. Quadrilateral internal angles and Theorem: The internal angles of quadrilaterals are 360°. Known: Quadrilateral ABCD, Proof: ∠A+∠B+∠C+∠D=360°. Note: For ease of writing, note The inner angle of the triangle is ∑,