表达式2: "g" left parenthesis, cos left parenthesis, "x" , right parenthesis , right parenthesis times "g" left parenthesis, cos left parenthesis, "v" , right parenthesis , right parenthesis left brace, negative StartFraction, pi Over 2 , EndFraction less than or equal to "x" less than or equal to StartFraction, pi Over 2 , EndFraction , right bracegcosx·gcosv−π2≤x≤π2