Question

I dont even know where to start or what to ask i would like to understand how to solve this so that i can explain to my kid.

Answer 1

9514 1404 393

Answer:

  A. perhaps 0 to 7 days

  B. the radius in mm at the start of the study

  C. 0.114 mm/day

Step-by-step explanation:

A. It is always problematic to determine the reasonable domain for an exponential growth function. You can always limit the domain to the length of time for which the function is said to model the growth. It is difficult to say how much beyond that time period the exponential growth can be extrapolated, as most systems run into limits to growth.

Here, the base of the exponential term is 1.01 = 1 + 1%. This tells you the growth rate is 1% per day. The study concludes when the radius was 11.79/11.00 = 1.071818... ≈ 1 + 7.2% times the original size. That is, the study lasted approximately 7 days.

The question in part C has you look at the size on day 7, which is apparently the last day of the study. It is not clear that the model is at all useful beyond the end of the period it is intended to describe.

A reasonable domain for the growth function is 0 to 7 days.

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B. The function gives the radius of the algae after d days. When d=0 (the y-intercept), the function gives the radius of the algae after 0 days. That is the meaning of the y-intercept is the initial radius of the algae (at the beginning of the study).

The y-intercept is always the "initial value", the value when the independent variable is zero. You have to look at the function definition to see what it is the initial value of.

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C. The average rate of change is the difference in function values divided by the difference in time between them. Here, the attached table tells us that is ...

  (f(7) -f(2))/(7 -2) = (11.793 -11.221)/5 = 0.572/5 = 0.1144 . . . mm/day

The units of the "average rate of change" are the units of the slope of the curve on the graph: the y-axis units divided by the x-axis units. Here, that is mm/day.