Fix bug 4691

Author: gajennings

OpenProblemLibrary/AlfredUniv/anton8e/chapter15/15_7/prob3.pg

@@ -25,7 +25,7 @@ DOCUMENT();        # This should be the first executable line in the problem.
 
 loadMacros(
   "PGstandard.pl",
-  "PGchoicemacros.pl",
+#  "PGchoicemacros.pl",
   "unionTables.pl",
   "Alfredmacros.pl",
   "MathObjects.pl",
@@ -48,7 +48,7 @@ $b = random(3,10);
 $r = sqrt($b/$a);
 
 $upper = Formula("$b-$a*x^2-$a*y^2")->reduce;
-$ans = Real(2*pi*$n/(2*$n+2)*($b/$a)**(($n+1)/$n));
+$ans = Compute("2*pi*(($b*$n)/(2*$n+2)($b/$a)^(($n+1)/$n)-($a*$n)/(4*$n+2)*($b/$a)^((2*$n+1)/$n))");
 
 #######################################################
 # Prevent students from being able to double click in