Consider the function below. (If you need to use -infinity or infinity, enter -INFINITY or INFINITY.)
f(x) = sqrt(x^2+3) - x
(a) Find the horizontal asymptote.
y = _____________
(b) Find the interval where the function is decreasing.
( _________, ____________)
(c) Find the interval where the function is concave up.
( _________, __________)