研究梯形问题常常要视已知条件添加某些辅助线,把梯形问题转化为三角形或平行四边形(或矩形)问题,从而使分散的条件适当集中,找出原问题的答案·一、当已知条件中含梯形两腰或同一底上两角时,可平移一腰或过上底两端点作高,把梯形转化为平行四边形和三角形来解;或延长两腰,把梯 Studying trapezoidal problems often involves adding certain auxiliary lines depending on known conditions, transforming trapezoidal problems into triangular or parallelogram (or rectangular) problems, so that the scattered conditions are properly concentrated and the answers to the original questions are found. When the conditions include trapezoidal two waists or two corners on the same bottom, you can shift the waist up or over the two points at the bottom to make a high, transform the trapezoid into parallelograms and triangles to solve; or extend the two waists, take the ladder