Question

已知集合A={x |x^2-3x+2=0} ,B={x |x^2+2(a+1)x+(a^2-5)=0},若A∩B={2},求a取值范

若A∩B={2},求a取值范围

Answer 1

由题意A={1,2}且2属于B，但1不属于B
也就是x=2时方程x^2+2(a+1)x+(a^2-5)=0成立
将2代入得4+4(a+1)+(a^2-5)=0
a^2+4a+3=0
得a=-1或-3

Answer 2

当X=2，x^2+2(a+1)x+(a^2-5)=4+4（a+1）+(a^2-5）=0
解得a=-1或a=-3

Answer 3

这因该是求a得值吧，a=-1