Question

x的平方+ xy +2x=44,y的平方+ xy+ 2y=-41,求x y的值

Answer 1

①+②得

x^2+2xy+y^2+2(x+y)+1=4

(x+y+1)^2=4

得x+y=1或-3

①-②得

（x-y)(x+y+2)=85

x-y=85/3或-85

∴x=44/3,y=-41/3或x=-44,y=41