Fixed TeX error, and did some code cleanup.
Fixed broken link (and minor cleanups).
Changed \{x_n\} to $LB x_n $RB; other cleanup.
Enlarge answer blanks
Clarified the question, and made the solution agree with the answer.
The problem should recognize that the formula is valid when n>1 (the 0th partial sum is 0, not $b/$d)
Fix bug "Could not generate enough valid points" with random seed 216.
Fix wrong answer on second part (random seed 63), and minor text changes
Make instructions agree with required answer.
Add more details in the problem statement, and add keyword 'separated'.
Add clarifying commend "Enter your answer as y=... ."
Clarify that the differential equation is for x>0, and make it not reject answers like C|x|^5.
Change the integrand to one that is not easily evaluated.