(1)、x-1≠0,则x≠1
又x+4≥0
x≥-4
f(x)的定义域为x≥-4且x≠1
(2)、f(-1)=6/-1-1-根号-1+4
=-3-根号3
f(12)=6/12-1-根号12+4
=6/11-4