A＝｛x｜x＾2＋4x＝0 }
={ x| x(x+4) =0 }
= {-4,0}
A∩B＝B => B is subset of A
for x =0
a＾2－1=0
a = 1 or -1
for x= -4
16- 8(a+1)+ a^2-1=0
a^2-8a+7 =0
(a-1)(a-7)=0
a = 1 or 7
ie a= -1, 1 or 7 #