高一数学集合方面的两个题,

1.f[f(x)]=m[mx/(4x-3)]/{4[mx/(4x-3)]-3}
=m²x/[4mx-3(4x-3)]
=m²x/(4mx-12x+9)=x
m²x=(4m-12)x²+9x
4(m-3)x=m²-9=(m-3)(m+3)恒成立
则m=3
2.x²+4x=0 x(x+4)=0
解得x=0或-4
所以A={0,-4}
如果A∪B=A
1.B为空集时,方程无解
判别式=[2(a+1)]²-4(a²-1)