Applications of Trig functions in Economics? Are there any applications of trig functions (ie $\sin(x)$, $\cos(x)$,$\tan(x)$) in economics?
The main property of trig functions is their cyclicality. Then one would think that they could be ideal in time series analysis, to model "fluctuations around a trend". I believe that the reasons they are not actually used in such a setting are 

1) They are deterministic functions, so they do not allow for fluctuations to be stochastic

2) If the researcher wants to create a model that produces up and down fluctuations (oscillations) around a trend, he would want to obtain that property from the behavioral and other assumptions of the model. If he were to use a trig function, he would a priori impose on the model the sought theoretical outcome.

Instead, one opts for difference-differential equations. There we obtain oscillations (damped or not) if some characteristic roots are complex -and then the trig functions appear, but as an alternative representation, not as buidling blocks.