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**MathBane** Poiseuille's law describes the velocities of fluids flowing in a tube—for example, the flow of blood in a vein. This law applies when the velocities are not too large—more specifically, when the flow has no turbulence. In this case the flow is *laminar*, which means that the paths of the flow are all parallel to the tube walls. The law states that $\displaystyle v=k(R^2-r^2)$, where *v* is the velocity, *k* is a constant (which depends on the fluid, the tube, and the units used for measurement), *R* is the radius of the tube, and *r* is the distance from the centerline of the tube. Since *k* and *R* are fixed for any application, *v* is a function of *r* alone, and the formula gives the velocity at a point of distance *r* from the centerline of the tube

(a) What is *r* for a point along the walls of the tube?

(In so many words, this basicly means to get r by itself, right?)

(b) What is the velocity of the fluid along the walls of the tube?

(...Wait, it didn't give me a value? I'm going to take a wild guess and say the fluid along the wall is zero.)