Give an example of a function whose domain is [2,infinity).

Answer 1

Not totally familiar with the terminology of
[2, infinity] , don't know if the 2 is included or not

If the 2 in included, how about

f(x) = √(x-2)

if the 2 is excluded, we would use something like
f(x) = 5/√(x-2)

Answer 2

5x-2