How seasonal components can be represented as sinusoids in a regression model.

There was a verbal solution given to this problem in the members only section. I'm not sure if its "legal" to share the whole thing, but here is an excerpt of the solution. " The time series has a weekly periodicity with two peaks: Monday and Thursday, corresponding respectively to the publication of the Monday and Thursday digests. The impact of the Monday and Thursday email blasts extent over the next day; this makes measuring the yield more difficult, unless you use additional data, e.g. from our newsletter vendor. However, the bulk of the impact is really on Monday and Thursday."