I know that "until now" indicates that something changed.
No messages have come until now. Now the first message arrived.
But what about using it in the past, for example in reported speech or just meaning in the past?
It was not clear to me until now. The whole sentence is meant to refer to past, e.g. describing what happened during my studies.
I did not know much about trigonometry. So far, I was only using algebra. When I was young.
Best Answer
If I am understanding you correctly, you want to place an entire sentence in the past.
There are several ways to do this. Using the first example, in speech, many people use the simplest forms to speak, so
But writing is a bit more formal, so I would take your main verb, was/be and look at the past tenses: you want the past, you want it to have been done/finished in the past, so you want to look at least at the past pluperfect of be, third person, singular):
Do the same to your second example:
I did not know much about trigonometry is fine, it's all in the past. So change the second sentence.
So far, I was only using algebra. (This is a bit incorrect, because your words, so far, and was using indicates a continuous action, so was doesn't match it in tense.
Be, past participle: been; pluperfect: had been + using (continuous) =
So far, I had only been using algebra. (For style reasons, I would change So far to Up to that point or something like it.)
Don't feel discouraged if you can't speak like that yet. Most conversations are informal, and it's all put in a simpler past.