x²+y²-4x+6y+13=0x²-4x+4+y²+6y+9=0(x-2)²+(y+3)²=0∴x-2=0 y+3=0∴x=2 y=-3 （3x+y)²-3（3x-y)(x+y)-(x-3y)(x+3y)=9x²+6xy+y²-9x²-6xy+3y²-x²+9y²=13y²=13×9=117
