x²+4y²=2x+4y-2移项得x²-2x+1+4y²-4y+1=0(x-1)²+(2y-1)²=0因为 (x-1)²和 (2y-1)²都为非负数所以 (x-1)²=0,(2y-1)²=0则x=1,2y=1,x=2y所以√(x-2y)=√0=0...