I think I'm on the verge of a breakthrough on this problem, but it's just not coming. Please tell me where my approach goes wrong or whether I'm correct but don't know how to integrate the resulting equation properly. The problem reads: A circular disk of radius r and thickness d is made of material with resistivity p. Show that the resistance between the points a and b (a is the front of the curved side of the cylinder and b is the backside) is independent of the radius and is given by R = [pi]p/2d. I start out with R = pL/A where L is length and A is the surface area perpendicular to the direction of the flow of the charges. dR = pdx/A A = d * the width of the rectangular surface area for the little sliver of the cylinder, which is given by the equation of the circle y = 2[squ] (r^2-(x-r)^2). Is this correct? I then integrate R = p/2d[inte] dx/[squ](r^2-(x-r)^2) from 0 to 2r? This gives me R= [pi]pr^2/8d. Obviously wrong!!! Any suggestions would be greatly appreciated. Thanks.