Natural Gas Usage The table shows the average amount of natural gas in thermal units...

Natural Gas Usage The table shows the average amount of natural gas in thermal units per day used by a residential natural gas customer in Reno, Nevada. (The data represent 15 months.)

a. Explain why the data should be cyclic.

b. Align the first January to x = 1 and write a sine model for the data.

c. What period does the model indicate? How does this period affect extrapolations using this model?