Negation of "A and B"

moreglnn

I really don’t understand where this rule ” For conditionals, A and B negates to A → /B ” came from or how it would be applicable to the actual exam. This comes from the Negation skill builder in the Logic of Intersecting Sets module. It was never stated beforehand in neither the negating conditional statements or elsewhere, at least to my knowledge. I understand it intuitively as you’re saying that rather than both A and B being true simultaneously, you’re positing that /B is a necessary condition of A and thus can’t exist together. However, we previously learned about negation of the conjunction “and” in conditional relationships as being A and B → C negated to /C → /A or /B as specified by De Morgan’s law. I guess I’m just struggling to see, how to tell the difference or when/how to use this new rule in context with a question on the LSAT. Is the rule just referring to when you have both premises A and B as part of the argument a way to negate it, is by using that rule. Like I don't see how just A and B can exist on their own in question. I feel like there must be either A and B -> C or C -> A and B included when encountering this in a question. Greatly appreciate any comments or help someone could add!

Help