f(x)=√(21-4x-x²),算术平方根有意义,21-4x-x²≥0x²+4x-21≤0(x+7)(x-3)≤0-7≤x≤3A={x|-7≤x≤3,x∈R}.y=log2(x-a+1),对数有意义,x-a+1>0 x>a-1B={x|x>a-1,x∈R}.(1)A包含于B,则a-1...