A linear regression model for the braking distance y y\,y metres of a car travelling at speed x x\,x km/h is y=0.011x2+0.18x−2.4y=0.011x^2+0.18x-2.4y=0.011x2+0.18x−2.4, for 40≤x≤10040\leq x\leq10040≤x≤100.
Use the model to estimate the braking distance at 80 km/h.
Explain why the model should not be used to estimate the braking distance at 130 km/h.
A car travelling at 80 km/h has an observed braking distance of 86 m. Find its residual.