当x=1,y=-2时,代数式x-(x+y)+(x+2y)-(x+3Y)+……-(x+99y)

当x=1,y=-2时,代数式x-(x+y)+(x+2y)-(x+3Y)+……-(x+99y)
当x=1,y=-2时,代数式x-(x+y)+(x+2y)-(x+3Y)+……-(x+99y)

当x=1,y=-2时,代数式x-(x+y)+(x+2y)-(x+3Y)+……-(x+99y)
x-(x+y)+(x+2y)-(x+3y)+……-(x+99y)
=x-x+x-x+...+(2y-y)+(4y-3y)+...+(98y-97y)-99y
=49y-99y
=-50y
=-50×(-2)
=100

每两项合并得-y共100项所以结果是-50y

x-(x+y)+(x+2y)-(x+3Y)+……-(x+99y)
=[x-(x+y)]+[(x+2y)-(x+3Y)]+……[(x+98y)-(x+99y) ] 分成50组
=-y-y……-y
=-50y
=100

原代数式等于x-x-y+x+2y-x-3y+......-x-99y等于-y+2y-3y+......-99y等于-50y,然后把y等于-2带入，得100 ..
所以最后次代数式为100