They aren’t. It’s easy to mistake the three rolls as three faces of the same thing, because they each involve rolling a d20, adding any modifiers, and comparing the total to a Difficulty Class, and they’re all subject to advantage and disadvantage. In short, they share the same procedure for determining success or failure.
Despite this common procedure, the three rolls are separate from each other. If something in the game, like the guidance spell, affects one of them, the other two aren’t affected unless the rules specifically say so. The next few questions touch on this point again.