Question

设集合A＝｛x|x的平方－x－2＝0｝,B＝｛x|ax＝4｝,已知B⊆A,求实数a的值

Answer 1

A={x|x^2-x-2=0}

={2,-1}

if B is subset of A

when x=2

a(2)=4

a=2

when x=-1

-a=4

a=-4