Union of 2 Sets

 
    Here 
    A={2,5,7} 
    B={1,2,5,8} 
     
    HERE the common elements are 2,5 
    Union is 1,2,5,8,7  
  
 
     

Union of 3 sets
     
 
      
    Here 
    X={1,2,5,7,8} 
    y={2,3,5,7,9} 
    z={4,5,7,8,9} 
   Now the union is 1,2,3,4,5,7,8,9