Please clarify me on the following. When I specify a number, parameter, factor and so on, what is the right article to be used? For example, "the or a factor of 5 ... / the or a ratio of 4 to 3 .../ the or an angle of 90 ../.
Since the number is specified I though that "the" should be used as opposed to the cases: a proportion around/ close to 2/ so on. But there are also many cases when a particular number is specified, but nevertheless "a" is used as if there is some uncertainty. "An angle with a measure of 90". Please help me with this rule. Thank you a lot, Sincerely yours, Alexander