Question

若x2+y2-6y+4x+13=0，则x2-y2=______．

Answer 1

x的平方加y的平方减4x加6y加13等于0

x^2 + y^2 -4x +6y +13=0

(x^2 - 4x + 4) +(y^2 +6y +9=0

(x-2)^2 +(y+3)^2 =0

x-2 =0, y+3 =0

x=2, y= -3

x^2-y^2 =4-9=-5