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

问题描述:

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

原式=x-x+x-x+…+(2y-y)+(4y-3y)+…+(98y-97y)-99y
=49y-99y
=-50y,
当x=1,y=-2时,原式=-50×(-2)=100.
故答案为:100.