I want my students to enter the ordered pair for a polar coordinate using exact radian measures. How to I code it so that the student has to enter the answer as (4, -7pi/4)?
The recommended format is to use countNumberUsage and a range of values, so you would need to change your check to this:
check=my_x=4 and countNumberUsage(this.latex,4)=2 and (countNumberUsage(this.latex,-7)=1 or countNumberUsage(this.latex,7)=1) and my_y<-5.497 and my_y>-5.498
Because you are expecting an exact form (kind of like checking for spelling errors), you could possibly get away with replacing all of your code above with this LaTeX check for the whole point:
check=this.latex=`\left(4,-\frac{7\pi}{4}\right)` or this.latex=`\left(4,\frac{-7\pi}{4}\right)`
correct: check
Note that both ways would need to include the possibilities for the negative before or with 7.