Chapter 9, Problem 30RE

To determine

To calculate: The total revenue to the nearest $\$100$ be changing $20$ months from now using the technology for the sales department of OHaganBooks.com which predicts that the revenue from sales of the latest blockbuster Elvish for Dummies will vary in accordance with annual releases of episodes of the movie series “Lord of the Rings Episodes $9-12$ ”. It has come up with the model $R\left(t\right)=20,000+15,000e^{-0.12t}\cos \left[\frac{\pi }{6}\left(t-4\right)\right]$ dollars $0\le t\le 72$, where t is the time in months from now and $R\left(t\right)$ is the monthly revenue.