解析几何中涉及焦点及焦半径(椭圆、双曲线、抛物线上的一点与焦点的连线)、焦点弦(经过焦点的弦)的有关问题是一类基本的、常见的问题.对于这类问题,我们一般利用第一、第二定义,正、余弦定理等方法求解,熟练掌握有关结论并能加以灵活运用,将有效提高解题速度. The related problems in analytical geometry involving focus and focal radius (ellipse, hyperbola, connection between a point on the parabola and the focal point), and focus chord (chord through focus) are a basic and common problem. We generally use the first and second definitions, the positive and the cosine theorem to solve the problem, master the relevant conclusions and be able to use it flexibly, which will effectively increase the speed of problem solving.