以二次函数为载体的含90°角的动态存在问题是近年来中考的热点,由于动点的不确定性,加之对学生的知识运用及分析能力要求较高,有一点的难度.对这类题,一般可从勾股定理、构造K形图利用相似三角形、构造辅助圆利用直径所对的圆周角是直角这三个角度加以分析.一、利用勾股定理 The problem of dynamic existence of 90 ° angle with quadratic function as a carrier is a hot spot in the senior high school entrance examinations in recent years. Due to the uncertainty of the moving point and the high requirement of students’ knowledge and analysis ability, it is a bit difficult. In general, the Pythagorean theorem can be used to construct the K-diagram to use similar triangles and the constructional auxiliary circle to analyze the three angles from the angle at which the circular angle is right-angled. First,