(1)X1=1,X2=-1,X3=-1,X4=3,X5=3,X6=-3
(2)X1+X2+…+X8
=1-1-1+3+3-3-3+5
=4
(3)X1+X2+…+X2003+X2004
=1-1-1+3+3-3-3+5+5-5-5+.+1001+1001-1001-1001+1003
=1002
(1)X1=1,X2=-1,X3=-1,X4=3,X5=3,X6=-3
(2)X1+X2+…+X8
=1-1-1+3+3-3-3+5
=4
(3)X1+X2+…+X2003+X2004
=1-1-1+3+3-3-3+5+5-5-5+.+1001+1001-1001-1001+1003
=1002