Context :
My girlfriend (let's call her V) and I, are programmers, and sometimes we ask each other questions when we believe the other may have an answer.
A few times, she’s told me that I sounded patronizing in my answer (which might be the case, but I don't see how or why).
We usually never put punctuations at the end of our sentence, and when we do, it is usually a sign that an argument will start.
The exchange usually happens like this:
V: How do you do A by B?
Me: I don't know, I don't have the ecosystem on my computer to test it, but I believe the answer is C, let me check
Delay of 5 minutes or so.
Me: Ok the answer does seem to be C, according to this reference, this should work
V: How? Can you write it?
Me: (code solving A by B with C)
V: Ok thanks.
Me: Sorry for the delay, I was making sure I had the reference for it
V: Then you are very smart.
Me: Why are you upset?
V: Because you said like every dumb person would google that
[argument continues]
I believe something in the way I express myself in that particular interaction was definitely wrong, when I was saying that I was looking for reference.
However this is the way I usually interact with colleagues for technical questions and when I answer on Stack Overflow I make sure I have the right reference to back my answer.
I know we are talking about interactions with my girlfriend, but on technical issues I was assuming we were interacting like we would in a work fashion. Maybe this is my mistake.
So, my question: how can I answer such a question without sounding like a patronizing guy, that has all the information?
EDIT
Thank you very much for your inputs, there are a lot of good recommendations in the answers to the question. There was a clear difference between the tone of my exchange with her here and our general interactions (but no part lacking in this dialogue).
Today we exchanged again about some programming topic and I used a tone we have more in our usual interactions and offered one solution that she looked up by herself and she found another solution. The general gist was to give what I honestly think is the answer and trust her research, helping further if needed.