What is the proper way to write the range of any constant function (such as f(x) = 6)? in interval notation?

Question

Can one use brackets? [6] or would it look like [6,6] or just list it as  6?

Answer 1

The range of the function is all the y values ... so if you are writing that in interval notation, you are correct,

You would write it as [6,6] ... the square brackets means you are including the endpoints.  The interval starts and ends at 6.