If I am understanding you correctly, you want to place an entire sentence in the past.
It was not clear to me until now.
I did not know much about trigonometry. So far, I was only using algebra.
There are several ways to do this. Using the first example, in speech, many people use the simplest forms to speak, so
It was not clear to me until then/that point...
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):
It had not been clear to me until then (or choose your pint in the past when it became clear: that moment, until I had finished the semester, whenever.)
Do the same to your second example:
I did not know much about trigonometry. So far, I was only using algebra.
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.)
I did not know much about trigonometry. Back then, I had only been using algebra.
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.
I didn't know much about trigonometry. Back then, I only knew Algebra/was only using.
Best Answer
Yes, your first sentence should be in the past tense. The tenses of your sentences should agree. Maybe this year the number of Asian students has risen markedly, but it's not important now -- it might have been when you went there, though.
I wonder what kind of school you're talking about. Sounds like a college because you were already driving.
I'd revise the first sentence to read:
I'm assuming that this was in an anglophone country, probably the USA (because of the car reference).
I'd revise the second sentence to read:
You don't want to sound helpless by saying that because you had no car, you couldn't go anywhere off campus. I added "isolated" to "rural" because, if you didn't leave the campus solely because you had no car, it means that there was no local town within walking distance and no public transportation. It's necessary to think a little bit more about the implications of what you say and how you say it.