Medium fix.
Merge pull request #51 from Dick-Lane/master

Replace "sin" with "\sin" in first line of Solution.
Fix bug?
Merge branch 'master' of github.com:openwebwork/webwork-open-problem-library
Update graph

Add a blue segment along the x- and y-axes.
Update graph

Add blue segment to x- and y-axes.
Finish fixing bug 2880
Small fix of randomization.
Put expression into math mode to avoid warning when hardcopy is generated.
Also use displaystyle for a fraction.