Fix bug 4681

Author: gajennings

OpenProblemLibrary/Michigan/gateways/derivative/topic_trig_func_logs/prob54.pg

@@ -25,7 +25,7 @@ $ans = "2*(5)*sin(4*x)*cos(4*x)^(-9/4)";
 
 Context()->texStrings;
 BEGIN_TEXT
-Differentiate \(V = \displaystyle{2 \over \cos(4 x)^{5/4}}\)
+Differentiate \(V = \displaystyle{2 \over [\cos(4 x)]^{5/4}}\)
 $BR
 Answer: \( {dV\over dx} = \) \{ans_rule(55)\}
 END_TEXT