初中数学（难）

解：由题意知：
(x +y)^2=4
故：x +y = 2或 x +y = -2
又x^2 -y^2 = (x +y)(x -y) =5
故：x -y = 2.5 或x -y= -2.5

x^2-y^2=(x+y)*(x-y)=5 (1)
(x+y)^2=4 (2)

（1）除以（2）==> (x-y)/(x+y)=5/4 ==>x=-9y
==> (x+y)^2=(8y)^2=4 ==> y=1/16
==>x-y = -10y = -10/16

x平方-y平方=5变为(x-y)(x+y)=5，，(x+y)的平方=4变为x+y=2，所以x-y=5/2=2.5

(X-Y)(X+Y)=5
(X+Y)(Y+X)=4
所以X-Y=5/2,-5/2