在近几年全国各省市的中考以及初中数学竞赛中,我们经常会看到这样一类数学问题,在平面直角坐标系中,判定两条直线是否垂直,或者一个三角形是否是直角三角形.这里我们介绍三种处理此类问题的方法.(2014宜宾)如图,已知抛物线y=x2+bx+c的顶点坐标为M(0,-1),与x轴交于A、B两点.过原点的 In the middle schools and middle school mathematics competitions of various provinces and cities in China in recent years, we often see such a kind of mathematical problem that we determine whether the two straight lines are perpendicular or not in a plane rectangular coordinate system. (Yibin 2014) As shown in the figure, the vertex coordinate of the parabola y = x2 + bx + c is M (0, -1), and is intersected with the x axis at points A and B. Over the origin