Small-angle approximation
（重定向自Small angle approximation）
![Approximately equal behavior of some (trigonometric) functions for x → 0](/Images/godic/202502/11/Kleinwinkelnaeherungen3406.png")
![](/Images/godic/202502/11/Small_angle_compair_odd.svg3406.png")
![](/Images/godic/202502/11/Small_angle_compare_even.svg3406.png")
![](/Images/godic/202502/11/Small_angle_triangle.svg3406.png")
The small-angle approximation is a useful simplification of the basic trigonometric functions which is approximately true in the limit where the angle approaches zero. They are truncations of the Taylor series for the basic trigonometric functions to a second-order approximation. This truncation gives: