  
 n=1   
 
    6.4207278  
 
 n=2   
 
    6.3912102  
 
 n=4   
 
    6.3891937  
 
 The exact value of intergation is :   
 
    6.3890561  
 
 thus corresponding errors are :    
 
  - 0.0316717  
  - 0.0021541  
  - 0.0001376  