Update 8.4.md

Same problem with my last edit. It should be divided by n, not 10, as we have n inputs and want to achieve uniform distribution by radius, so we split the radii into sub-intervals in the range (0,1]

docs/Chap08/8.4.md

@@ -49,8 +49,8 @@ Bucket sort by radius,
 
 $$
 \begin{aligned}
-\pi r_i^2 & = \frac{i}{10} \cdot \pi 1^2 \\\\
-r_i & = \sqrt{\frac{i}{10}}.
+\pi r_i^2 & = \frac{i}{n} \cdot \pi 1^2 \\\\
+r_i & = \sqrt{\frac{i}{n}}.
 \end{aligned}
 $$