x＋y=﹣1
(x+y)^2=(-1)^2
x^2+2xy+y^2=1
x^2+y^2=1-2xy=1-2*(-6)=13
(x-y)^2
=x^2-2xy+y^2
=x^2+y^2-2xy
=13-2*(-6)
=25
x-y=±5