The circulation C of a certain magazine as a function of time t is given by the formula

  

      

  

Here C is measured in thousands, and t is measured in years since the beginning of 2006, when the magazine was started. 

  

a. Make a graph of C versus t covering the first 6 years of the magazine’s existence. 

  

b. Express using functional notation the circulation of the magazine 18 months after it was started, and then find that value. 

  

c. Over what time interval is the graph of C concave up? Explain your answer in practical terms. 

  

d. At what time was the circulation increasing the fastest? 

  

e. Determine the limiting value for C. Explain your answer in practical terms.     
 

5.2 C = 0.1 + 0.3