I read a few articles that explained knowledge as being a subset of beliefs. For instance, here's one explanation from Knowledge | Internet Encyclopedia of Philosophy (utm.edu):
So, three distinct phenomena are identified (even if only in a generic way), before being combined. And that combination is being said to be what any — and only any — case of knowledge exemplifies. Knowledge is a belief; but not just any belief. Knowledge is always a true belief; but not just any true belief. (A confident although hopelessly uninformed belief as to which horse will win — or even has won — a particular race is not knowledge, even if the belief is true.) Knowledge is always a well justified true belief — any well justified true belief. (And thus we have the justified-true-belief conception of knowledge.)

I really like this explanation but my thinking has always been that knowledge and beliefs are different. I can accept that it is not completely different in that there are similarities, but I thought there were aspects of knowledge that are mutually exclusive to belief, such as the level of certainty, or the basis for accepting some proposition as true. If knowledge contains an aspect that is mutually exclusive to belief, then it can not be said to be a type or subset of belief. For example, {1,2,3} is a subset of the set {1,2,3,4,5}. But if knowledge is represented as {1,2,6,7} then it can not be said to be a subset of {1,2,3,4,5} (this set stands for beliefs). Also, in explaining the difference between atheism and agnosticism, don't people always explain that difference by drawing a distinction between 'belief' and 'knowledge'?

Given this background info., is it correct to say that knowledge is a subset of belief?

Are the mutually exclusive examples that I brought up between the two terms (e.g. level of certainty, etc.) just a matter of semantics?

One possible evidence that may help the situation is by showing if someone can know something without believing it? If possible that would mean you can have knowledge without belief. Perhaps there are other scenarios that can be used as evidence.