The question is.
The speed of air escaping through your trachea when you cough is a function of the force due to chest contraction and the size of the trachea. It can be modelled by the equation
S = F(1+0.9r^2-r^3) where F is the constant force of youre chest contraction, r is the radius of your trachiea in centimeters, S is the speed of the airflow.
Determine the max speed of airflow.
I know to find the max speed I need to take the derivative and find critical numbers, but how do I do that when there is the F and the r??