When blood flows along a blood vessel, the flux f (the volume of blood per unit time that flows past a given point) is proportional to the fourth power of the radius r of the blood vessel.

that is, f = kr4 where k is some constant. this is known as poiseuille's law. show that the relative change in f (that is, df / f) is about four time the relative change in r.

how will a 5% increase or decrease in the radius of the artery affect the flow of blood?