我们知道,直径所对的圆周角是直角,反之,90°的圆周角所对的弦是直径.由此可见,直角(或垂直)与直径有着密切关系,要善于把它们联系起来处理问题,既要见直角(或垂直)想直径,又要遇直径思垂直.特别是当题中涉及直角(或垂直),直角顶点的位置不确定,但其对边即斜边确定时,可以斜边为直径构造辅助圆,放在圆中来考虑解决.现举三例,供学习参考. We know that the diameter of the circle of the right angle is a right angle, on the contrary, 90 ° of the circumferential angle of the string is the diameter of the diameter.Thus, right angle (or vertical) is closely related with the diameter, we should be good at linking them to solve the problem, It is necessary to see the right angle (or vertical) to the diameter, but also the case of vertical thinking D. Especially when the title involves right angle (or vertical), the location of the right angle vertex is uncertain, Auxiliary circle for the diameter of the structure, put in the circle to consider the solution. Now cite three cases for learning reference.