1.三角函数的定义大家都知道,在现行的中学平面三角课本里,我们是利用点的直角坐标来定义普遍角的三角西数的.这时我们取角 a 的顶点作为直角坐标系的原点 O,取角 a 的始边作为正半横坐标轴 OX(图1).然后在角 a 的终边上任意取一个点 P.设 OP 的长度是 r,点 P 的坐标是x 和 y.角 a 的6个三角函数就用这样三个 1. The definition of trigonometric function We all know that in the current middle school plane triangle textbook, we use the Cartesian coordinates of the point to define the triangle of the universal angle. At this time, we take the vertex of the angle a as the origin of the Cartesian coordinate system. , Take the beginning of the angle a as the positive semi-axis OX (Figure 1). Then take a point P on the end of the angle a. Let the length of the OP be r and the coordinates of the point P be the x and y angles. The six trigonometric functions of a use these three