5X²-4XY+Y²+2X+1=4x²-4xy+y²+x²-2x+1=(2x-y)²+(x-1)²=0至此，因为(2x-y)²，(x-1)²都大于零，所以(2x-y)²，(x-1)²都只能等于0(2x-y)²=(x-1)²2x-y=x-1X-Y=-1（-1）^2005=-1
