三角函数线是单位圆中用来表示三角函数值的有向线段.中学课本中讲了正弦线、余弦线和正切线,这些在单位圆中的线段的长度表示三角函数值的绝对值,它们的方向表示三角函数值的符号(向上或向右为正,向下或向左为负),即这些三角函数线的数量就等于其对应角的三角函数值.课本中三? The trigonometric function line is a directed line segment used to represent trigonometric function values ​​in the unit circle. In middle school textbooks, sine, cosine, and tangent lines are spoken. The lengths of the line segments in the unit circle represent the absolute values ​​of trigonometric functions. The direction indicates the sign of the trigonometric function value (upward or rightward is positive, downward or leftward is negative), ie the number of these trigonometric function lines is equal to the trigonometric function value of its corresponding angle.