x=(-1)^m=-1或1
x=-1时,x+2x^2+3x^3+…+999x^999+1000x^1000=-1+2-3+4+…-999+1000=500；
x=1时,x+2x^2+3x^3+…+999x^999+1000x^1000=1001*500=500500