我们知道 ,圆与椭圆的参数方程与三角函数有密切的联系 .对一些具有平方和形式的问题 ,利用圆与椭圆的参数方程 ,能使问题的解决简便快捷 .一、求轨迹问题例 1　已知点Ｐ是圆ｘ2 + ｙ2 =16上的一个动点 ,点Ａ是ｘ轴上的定点 ,坐标为 (12 ,0 ) ,当点Ｐ在圆上运动时 ,线段ＰＡ的? We know that the parametric equations of the circle and the ellipse are closely related to the trigonometric functions. For some problems with square sums, the parametric equations of the circle and the ellipse can be used to solve the problem simply and quickly. First, find the trajectory problem Example 1 The knowledge point P is a moving point on the circle x2 + y2 =16. Point A is the fixed point on the x-axis and the coordinate is (12,0). When the point P moves on the circle, the line segment PA?