①(a-b+c)(-a+b+c)=[c+(a-b)][c-(a-b)=c²-(a-b)²=c²-a²+2ab-b²②(3a+b-2)(3a-b+2)=[(3a+(b-2)][3a-(b-2)]=9a²-(b-2)²=9a²-b²+4b-4③(x+2y-3z)(x-2y+3z)=[x+(2y-3z)][(...