# QUIZ: Applications of Cubic Functions Part 2 y x

QUIZ: Applications of Cubic Functions Part 2 The data in the table give the average speed y (in knots) of the Trident motor yacht for several different engine speeds x (in hundreds of revolutions per minute, or RPMs) Engine Speed, x Boat Speed, y 9 6.43 11 13 15 17 19 21.5 LABEL THE X AND Y AXES. 7.61 8.82 9.86 10.88 12.36 15.24 Create a scatterplot (Boat Speed vs. Engine Speed) of the data in Excel and paste your graph below. Be sure to include a TITLE for your graph and Find a quadratic regression model (

y

ax

2 

bx

c

) for the data and report the model below. What is the value of r-squared for this model?  Find a cubic regression model (

y

ax

3 

bx

2 

cx

d

) for the data and report the model below. What is the value of r-squared for this model?  Which model is a better fit for the data? How do you know? Estimate the average boat speed of the Trident for an engine speed of 2400 RPMs. (Hint: 2400 RPMs would equal an x value of 24 since the equation denotes engine speed in hundreds of revolutions per minute.)