Answer:
f(x) ≈ −2.42x3 + 15.89x2 − 7.55x + 12
Explanation:
Notice that the year data are evenly spaced. Check the first differences between the total number or units to see if the data set is linear.
First Differences
41 − 18 = 23
67 − 41 = 26
82 − 67 = 15
69 − 82 = −13
17 − 69 = −52
Because the first differences are not constant, a linear model is not the best model of the data. Check the second differences to see if the data set can be modeled by a quadratic function.
Second Differences
26 − 23 = 3
15 − 26 = −11
−13 − 15 = −28
−52 − (−13) = −39
Because the second differences of the independent variable are not constant, a quadratic model is not the best model of the data. Check the third differences to see if the data set can be modeled by a cubic function.
Third Differences
−11 − 3 = −14
−28 − (−11) = −17
−39 − (−28) = −11
The third differences are approximately the same so we will use a cubic function to represent the data.
Enter the data into a calculator. Plot the data and find the cubic regression equation that best models the data.
f(x) ≈ −2.42x3 + 15.89x2 − 7.55x + 12