TITLE: Prove that $ (\mathbb{Q}\times\mathbb{R})\cup (\mathbb{R}\times\mathbb{Q})$ is a locally connected and connected subspace of $\mathbb{R}^2$
QUESTION [7 upvotes]: The book I am using for my Introduction of Topology course is Principles of Topology by Fred H. Croom.

Prove that $A = (\mathbb{Q}\times\mathbb{R})\cup (\mathbb{R}\times\mathbb{Q})$ is a locally connected and connected subspace of $\mathbb{R}^2$

This is what I understand:

A space $X$ is connected provided that it cannot be written as the disjoint union of specifically two open sets.
A space $X$ is locally connected at a point $a$ in $X$ if every open set containing $a$ contains a connected open set which contains $a$. The space $X$ is locally connected provided that it is locally connected at each point.  
I'm aware that neither connected nor locally connected implies the other, nor do their negations. Meaning I would have to prove each.
Now the set of rationals is disconnected (in fact totally disconnected). $\mathbb{R}^2$ is connected and locally connected. 
$A \subseteq \mathbb{R}^2$

I'm a little stuck on how to approach this question; however, I do have a rough idea. 
To prove $A$ is connected, I can claim that $A$ is disconnected. Then there exists two nonempty set $U$ and $V$ such that $U\cup V=A$ and $U \cap V = \emptyset$. Thus $U$ and $V$ are clopen. Eventually, I should arrive at a contradiction because $\emptyset$ and $A$ are the only subsets of $A$ that are clopen, proving $A$ is connected. However I am not sure how to properly execute the approach.  
To prove $A$ is locally connected. I can claim the space $A$ has a local basis $\mathscr{B}_a$. I would need to prove that $\mathscr{B}_a$ consist of connected open sets, proving $A$ is locally connected. 
Am I on the right track? Any suggestions oh how I can proceed with my ideas? 


Sorry for the long read. If there are any mistakes in what I stated above, please let me know so I can correct it. I sincerely thank you for taking the time to read this question. I greatly appreciate any assistance you may provide.

REPLY [2 votes]: There are several possible approaches to this. As suggested by John Hughes, you could prove path-connectedness. Another approach is as follows: $A$ is the union of $$A_q=\{q\}\times\mathbb R\cup\mathbb R\times\{q\}$$ over all rationals $q\in\mathbb Q$. Now, remember the following:
Theorem. Suppose $(X_\lambda)_{\lambda\in\Lambda}$ is a family of connected sets such that $X_{\lambda_1}\cap X_{\lambda_2}$ is non-empty for all $\lambda_1,\lambda_2$. Then $\bigcup_{\lambda\in\Lambda}X_\lambda$ is connected.
It follows easily from this that $A_q$ are connected and that $\bigcup_{q\in\mathbb Q} A_q$ is connected.
Your can prove local connectedness using a similar approach: first observe that the neighborhood of any point contains a "square", then prove that this "square" is connected.