I agree with what TheRealLester says in his comment to you question. It would help if you provided the first part of the sentence as it may make a difference to the answers you are given. For the sake of convenience I will assume that the missing part of your sentence is, 'I had to', i.e.:
I had to memorize a list of math formulas whose applications I had no idea of.
This sentence makes sense, but you could probably rephrase it so that it is easier to understand. For example, you originally said, 'formulas whose applications I had no idea of'. This could be understood as meaning that you learnt a formula but did not know how to apply it, e.g. I know that
A = π r2, but I don't know what r represents, or that this is the formula for calculating the area within a circle.
You clarified this in your next sentence, which is not the sentence that you asked about, when you wrote, 'I didn't know how they were applied in real life'. This is an important piece of information that should appear in your original sentence.
Now, you are making two statements:
I had to memorize a list of math formulas.
I don't know how to apply them in real life.
These are essentially contradictory statements, so your final sentence should join them in a manner that shows this, e.g.
Although I had to memorize a list of math formulas, I had no idea how I would apply them in real life.
I had to memorize a list of math formulas, but I don't know how I would apply them in real life.