Chapter 2.3, Problem 71E

Medicine. The French physician Poiseuille was the first to discover that blood flows faster near the center of an artery than near the edge. Experimental evidence has shown that the rate of flow $v$ (in centimeters per second) at a point $x$ centimeters from the center of an artery (see the figure) is given by

$v=f\left(x\right)=1,000\left(0.04-x^2\right)0\le x\le 0.2$

Find the distance from the center that the rate of flow is $20$ centimeters per second. Round answer to two decimal places.