Okay... I'm really not trying to beat this thing to death, but I have a preliminary exam coming up soon, and I'm very nervous because I still feeling like I'm struggling with what should be the most basic of questions.

I DO know that, if the hyperplane is defined simply by one of the coordinates (for sake of example, say ), then the statement is true. On the complement of , we know that the coordinate is nonzero. Since we are in projective space, we may assume that (because in ; if we are restricting to points where , we may as well "normalize" our points by dividing through by ). In this case, after this normalization, we may define a map

This turns out to be an isomorphism .

Is there some sort of way I can generalize this to the complement of an arbitrary hyperplane (that is, to a set defined by the equation ,each )? Maybe some sort of (projective..) linear change of coordinates (which I don't know how to do...)? Would the mapping, for example, be a legal isomorphism on the points of , in which case I could apply the idea above? Or is there something completely different I should be looking at?

I'm sorry for posting this stuff over and over when it seems no one really is able to help anyway... but I'm.. well, don't wanna saydesperate, but... yea. I really feel like I am understanding the concepts, but I'm not able to apply them at all to solve anything.

EDIT: Am I asking this in the appropriate forum, or would another section be more appropriate? I just figure it would go here since it uses a good deal of abstract algebra...