Part A:
Given that the final radius of the algae was approximately 13.29 mm, we need to find the number of days (d) it took to reach this size. We can set up and solve for d in the given function:
f(d) = 7(1.06)^d = 13.29
Solving this equation for d gives approximately d = 14.2. This result implies that it took approximately 14.2 days for the algae to reach this radius. However, in practice, the domain might be whole numbers as we usually count days in integers.
Therefore, the reasonable domain to plot the growth function would be d = 0 (the beginning of the study) to d = 15 (just above 14.2, rounded up to the next whole number).
Part B:
The y-intercept of the function represents the value of f(d) when d = 0.
If we plug in d = 0 into the function, we get:
f(0) = 7(1.06)^0 = 7
Therefore, the y-intercept of the graph of the function f(d) represents the initial radius of the algae at the beginning of the biologist's study, which is 7 mm.
Part C:
The average rate of change of a function between two points (d1, f(d1)) and (d2, f(d2)) is given by the formula:
average rate of change = [f(d2) - f(d1)] / (d2 - d1)
For d1 = 4 and d2 = 11, this will give:
average rate of change = [f(11) - f(4)] / (11 - 4)
= [7(1.06)^11 - 7(1.06)^4] / 7
= [7(1.06)^11/7 - 7(1.06)^4/7]
= 1.06^11 - 1.06^4
This is the average rate of change of the function from d = 4 to d = 11. It represents the average increase in the radius of the algae per day over this interval.