Suppose f is a real valued function mapping the reals to the reals for which f(x+y) = f(s)f(y). Prove that f having a limit at zero implies f has a limit everywhere and that this limit is one if f is not identically zero
such that
We are given that
exists
Then
Thus,
so that
If then we have
Which means so that the
function is identically zero which not possible
So we must have and so
So that we must have
if the function is not identically zero
Moreover, the limit
exists everywhere because
Which is
as
We note that
a finite quantity and
from above
Thus,
is a finite quantity and so the limit
exists for all
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