（2x-1）²-9（x+1）²=(2x-1)^2-[3(x+1)]^2=[(2x-1)+3(x+1)][(2x-1)-3(x+1)]=(5x+2)(-x-4)=-(5x+2)(x+4)100²-99²+98²-97²+…+2²-1² =(100+99)(100-99)+(98+97)(98-97)+……(...