题目

已知直角，为直角，，，建立适当的坐标系，写出顶点，，的坐标，并求证斜边的中点到三个顶点的距离相等． 答案：解析:设为原点，方向为轴正半轴，方向为轴正半轴， 则由距离公式可得结论． He hurried to the restaurant , only ________ his girl friend had left. A. to tell         B. to be told     C. telling         D. told