Let the function which models the data be y(x) = ax² + bx + c
Apply the function to the first three data points a + b + c = 9 .(1) 4a + 2b + c = 9.5 (2) 9a + 3b + c = 10.25 (3)
Subtract (1) from (2). 3a + b = 0.5 or b = 0.5 - 3a (4) Subtract (1) from (3). 8a + 2b = 1.25 (5) Substitute (4) into (5). 8a + 2(0.5 - 3a) = 1.25 2a = 0.25 a = 0.125 From (4), b = 0.5-3*0.125 = 0.125 From (1), c = 9 - 0.125 - 0.125 = 8.75
The function is y = 8.75 + 0.125x + 0.125x²
Check that the function works for x=4,5,6,7. From the calculator, obtain y(4) = 11.25 Correct y(5) = 12.5 Correct y(6) = 14 Correct y(7) = 15.75 Correct