x²+y²-6x+8y+25=0(x²-6x+9)+(y²+8y+16)=0(x-3)²+(y+4)²=0∵ (x-3)²≥0,(y+4)²≥0∴ 只有(x-3)=0 而且(y+4)=0时,才有(x-3)²+(y+4)²=0x-3=0 且 y+4=0x=3 ,y=-4...