Disable Trig so students cannot enter cos(arctan(x))

as suggested by diglin.  I completely missed that one.

Author: lahvak

OpenProblemLibrary/AlfredUniv/anton8e/chapter1/1.5/prob9.pg

@@ -46,6 +46,7 @@ $ans1 = Formula("1/sqrt(x**2 + 1)")->reduce;
 $ans2 = Formula("sqrt(1-1/x**2)")->reduce;
 $ans2->{limits}=[1.1, 10];
 $ans2->{test_at}=[[-2],[-3]];
+Context()->functions->disable('Trig');
 
 Context()->texStrings;
 BEGIN_TEXT