Error: calculate is undefined

Hello-

My system is CRM 2011 Update RU 12 & RU 6.  I am trying to sum up several fields of currency into one field.  I am using the following js.  I keep getting an error with the field's customized event.  Field;cpdc_value1 Event:onchange Error:calculate is undefined.  Not sure how to correct this.

function calculate()

   {

   var value1 = Xrm.Page.entity.attributes.get['cpdc_value1'].getValue();

   var value2 = Xrm.Page.entity.attributes.get['cpdc_value2'].getValue();

   var value3 = Xrm.Page.entity.attributes.get['cpdc_value3'].getValue();

   var value4 = Xrm.Page.entity.attributes.get['cpdc_value4].getValue();

   var value5 = Xrm.Page.entity.attributes.get['cpdc_value5'].getValue(); 

   if(value1==null)return;
   if(value2==null)return;
   if(value3==null)return;
   if(value4==null)return;
   if(value5==null)return;

   var resulta = value1 + value2 + value3 + value4 + value5;

   Xrm.Page.entity.attributes.get['cpdc_resulta'].setValue(resulta) ;

   }