High Quality Content by WIKIPEDIA articles! Small-angle approximation is a useful simplification of the laws of trigonometry which is only approximately true for finite angles, but correct in the limit as the angle approaches zero. It involves linearization of the trigonometric functions (truncation of their Taylor series) so that, when the angle x is measured in radians,Small angle approximation is useful in many areas of physics, including electromagnetics, optics (where it forms the basis of the paraxial approximation), cartography, astronomy, and so on.