Question

1-2+3-4+5-6....+1997-1998+1999=?

等于多少

Answer 1

相邻2项组合起来
1999/2=999余1
因此有999组-1
结果为（-1）*999+1999=1000

Answer 2

1-2+3-4+5-6+....+1997-1998+1999
=(1-2)+(3-4)+(5-6)+....+(1997-1998)+1999
=(-1)+(-1)+(-1)+....+(-1)+1999
=(-999)+1999
=1999-999
1000

Answer 3

1-2+3-4+5-6....+1997-1998+1999=1000

Answer 4

1-2+3-4+5-6+..+1997-1998+1999 =(1-2)+(3-4)+(5-6)..+(1997-1998)+1999 =(1998/2)*(-1)+1999 =999*(-1)+1999 =-999+1999 =1000