Correct answer checking, improve parameter selection.
Remove TeX markup from PopUp.
Correct trig function in answer.
Improve previous fix, improve solution text.
Allow partially blank input as appropriate.
Make answer checking more flexible, correct wording in one problem
part, improve solution.
Correct erronious division by 2 for y-value in solution text.
Correct problem to avoid the case of a constant term in the calculated plane.
Improve answer checking, correct answer display, problem text.
Make answer checking more robust.
Merge branch 'master' of github.com:openwebwork/webwork-open-problem-library