Please note and remember that the letters/symbols ascribed to terms in a function, theorem, whatever, are never absolute, they are only relative. by this i mean any pair of letters

have no menaing unless they are related to each other -- otherwise, any choice of letter/symbols will work, such as

and

, etc.

Now look at this:

By comparing this relative to the statement of the binomial theorem, is not the

u see in the statement meant to mean

? is not the

equal to

?(Where the

and the

here are not the same, they're just referring to the same argument.)

so all in all, you really should not ever get attached to symbols or letters used to relate variables in a mathematical expression. they can be switched, twirled, and discarded if it suits the progression of the operations to make things simpler.