The first thing i did with this problem is to draw out the circle, cord of length l, a radius and D. I found R as the hypothenous, D as the adjacent side and L/2 as the the opposite.. Using pythagorean theorem and solve for L i get L= 2*sqrt(r^2-D^2). Next i said Fsub(X)(x)= L= 2*sqrt(r^2-D^2) and take its integral from 0 to 2r. This is just a thought dont know if its correct.
