domain of -9/2+t^2 and 1-4t/2+t
the way you typed the domain, which is your choice of x's you could use, is the set of real numbers for both expressions
if you meant something like
-9/(2+t^2) , since the denominator could never be zero is still the set of real numbers
if the 2nd is 1 - 4/(2+t), clearly t ≠ -2