Question

is y=2/7x proportional

Answer 1

Yes, it is. If a : b=c : d, then ad=bc. The opposite is true.

Now we can use this fact.

If y/1=2x/7, then 2x=7y. If 2x=7y, then x : y = 7 : 2.

Of course, any function in y=ax is proportional.