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In order for to make all things clear, let me to explain you what is written in your post (to avoid misunderstanding).
You are given the set of all real numbers R.
You consider all the pairs (x,y) of real numbers such that x <= y. It is your set A.
The set A is not a primary set of the consideration.
The primary set is R.
And the question is: IS IT TRUE THAT FOR EVERY x from R the pair (x,x) is in the relation A, i.e. x <= x ??
Now I am ready to answer.
This relation is reflexive.
To check it, you should make sure that for every real number x, the pair (x,x) is the relation.
In the terms of the given relation, it means to check that
for each real x, x <= x.
but it is clearly and obviously true for all real numbers.
Answered and proved.
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If you have difficulties in understanding this issue, look into this Wikipedia article
https://en.wikipedia.org/wiki/Reflexive_relation