若x²+y²-6y+4x+13=0,则x²-y ²=??
追答x^2+y^2-6y+4x+13=0
(x+2)^2+(y-3)^2=0
x+2=y-3=0
x=-2 y=3
所以x^2-y^2=4-9=-5
若x²+y²-6y+4x+13=0,则x²-y ²=?
追答x²+y²-6y+4x+13=0
化简左边为(x+2)² + (y-3)²=0,所以x+2=0,y-3=0;
解得x= -2,y=3
x²-y ²=4-9=-5
若x²+y²-6y+4x+13=0,则x²-y ²=?
追答x²+y²-6y+4x+13 = (x²+4x + 4) + (y²-6y+9) = (x+2)² + (y-3)² = 0
于是x=-2 y= 3
所以x²-y ² = 4-9 = -5