y=√(x^2-1)
x^2-1≥0
(x-1)(x+1)≥0
x≥1,或x≤-1
x∈(-∝,-1]∪[1,+∝)
y=√[(1-x)/(1+x)]
(1-x)/(1+x)≥0,1+x≠0
-1≤x≤1,且x≠-1
x∈(-1,1]
y=ln(x+1)
x+1>0,
x>-1
x∈(-1,+∝)