S = + + + + +          − + + + +    = + + + = P2 3 4 2013 2 3 1006 1007 1008 2013KHI ĐÓ

1 ... 1 ... ...

S = + + + + +          − + + + +    = + + + = P

2 3 4 2013 2 3 1006 1007 1008 2013

Khi đó : ( S P ) 2013 = 0 2013 = 0

 

− + + + +     = + + + +

100 1 ... ...