全集I={1.2a-4.a^2-a-3},A={a-1,1}.A的补集为{3}.那a的值是( ).
问题描述：
全集I={1.2a-4.a^2-a-3},A={a-1,1}.A的补集为{3}.那a的值是( ).
答
I = {1,2a-4, a^2-a-3 }A = {a-1, 1}case 1a-1 = 2a-4and a^2-a-3 =3=>a=3 and (a-3)(a+2) =0=>a=3 and a=3 or -2=> a=3case 22a-4 = 3 and a^2-a-3 = a-1=> a = 7/2anda^2-2a-2 =0=> a = 7/2and a ...