焦点F(0,4),c=4
y^2/a^2-x^2/b^2=1
渐近线y=±a/bx
x+y=0,
-a/b=1,a=b 另一条渐近线y=x
c^2=a^2+b^2=2a^2=4^2
a^2=8,b^2=8
y^2/8-x^2/8=1