Fix bug 4682

Author: gajennings

OpenProblemLibrary/Michigan/gateways/derivative/topic_symbolic/prob31.pg

@@ -17,15 +17,15 @@ $showPartialCorrectAnswers = 1;
 Context('Numeric');
 Context()->variables->are( a=>'Real',  b=>'Real',  c=>'Real',  p=>'Real');
 
-$ans = "(a*b)*cos(b*p + c)";
+$ans = "(c*b)*cos(b*p + a)";
 
 # for information about tutorial cgi, contact the UMich repository owner
 # $tut = htmlLink("http://[local location of tutorial cgi]" .
 # 		"gwderivtut?pnum=737","rule for constant multiples,"");
 
 Context()->texStrings;
 BEGIN_TEXT
-Differentiate \(B(p) = a \sin(b p + c)\), where \(a,b\) and \(c\) are constants
+Differentiate \(B(p) = c \sin(b p + a)\), where \(a,b\) and \(c\) are constants
 $BR
 Answer: \( B'(p) = \) \{ans_rule(55)\}
 END_TEXT