How to write a segment in topology

Question

I have a segment of lenght $2+\frac{1}{n}$ centered in the origin and it is a part of this set:

$A_n = \{ (x,y)\in R^2 : y = r_n x , r_n \in Q \}$

is it ok if i write:

$A = [0,2+\frac{1}{n}]$

thanks

Answer 1

Write $$A=[a,b]\times \{0\}.$$