Fourier series can be used to approximate any differentiable function using sin and cosin functions. The accuracy increases as more terms are included in the series.
As can be seen from the animation, the mean deviation greatly increases on non-differentiable points (in the given case, they are dis-continuous and hence non-differentiable).
As can be seen from the animation, the mean deviation greatly increases on non-differentiable points (in the given case, they are dis-continuous and hence non-differentiable).