Fixed TeX errors (unescaped # in TeX mode)
Fixed TeX errors:  unescaped '#' in TeX mode, and missing \right| .
Fixed PG error ($ $ --> \( \) ); clarified first answer blank.
Fixed TeX errors (misplaced alignment tabs '&')
Cleaned up TeX errors and typos in hint.
Fixed TeX errors in alignment.
Fixed TeX error (missing \right )
Fixed TeX errors and rewrote solution.
Merge remote-tracking branch 'upstream/master'
Merge pull request #88 from paulvojta/master

Fix numerous TeX errors