This is a very common assumption in Physics, e.g. https://en.wikipedia.org/wiki/Pendulum_(mathematics)#Small-angle_approximation https://en.wikipedia.org/wiki/P

This is a very common assumption in Physics, e.g. https://en.wikipedia.org/wiki/Pendulum_(mathematics)#Small-angle_approximation https://en.wikipedia.org/wiki/Pendulum_(mathematics)#Small-a... Whether it's appropriate in a numerical calculation obviously depends on the possible inputs and the acceptable error bars :)