x²+y²-4x-2y+8=(x²-4x+4)+(y²-2y+1)+3=(x-2)²+(y-1)²+3∵(x-2)²≥0,(y-1)²≥0∴当x=2时,y=1时,(x-2)²=0,(y-1)²=0此时(x-2)²+(y-1)²+3有最小值3∴多项...